DICTIONARY OFSCIENCE ANDTECHNOLOGY

Specialist dictionariesDictionary of Accounting 978 0 7136 8286 1Dictionary of Agriculture 978 0 7136 7778 2Dictionary of Aviation 978 0 7136 8734 7Dictionary of Banking and Finance 978 0 7136 7739 3Dictionary of Business 978 0 7136 7918 2Dictionary of Computing 978 0 7475 6622 9Dictionary of Economics 978 0 7136 8203 8Dictionary of Environment and Ecology 978 0 7475 7201 5Dictionary of Food Science and Nutrition 978 0 7136 7784 3Dictionary of Human Resources and Personnel Management 978 0 7136 8142 0Dictionary of ICT 978 0 7475 6990 9Dictionary of Information and Library Management 978 0 7136 7591 7Dictionary of Law 978 0 7136 8318 9Dictionary of Leisure, Travel and Tourism 978 0 7136 8545 9Dictionary of Marketing 978 0 7475 6621 2Dictionary of Media Studies 978 0 7136 7593 1Dictionary of Medical Terms 978 0 7136 7603 7Dictionary of Nursing 978 0 7136 8287 8Dictionary of Politics and Government 978 0 7475 7220 6Dictionary of Publishing and Printing 978 0 7136 7589 4Dictionary of Sport and Exercise Science 978 0 7136 7785 0

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Check Your English Vocabulary workbooksAcademic English 978 0 7136 8285 4Banking and Finance 978 0 7136 8250 2Business and Administration 978 0 7136 7916 8Computers and Information Technology 978 0 7136 7917 5Human Resources 978 0 7475 6997 8IELTS 978 0 7136 7604 4Law 978 0 7136 7592 4Living in the UK 978 0 7136 7914 4Medicine 978 0 7136 7590 0PET 978 0 7475 6627 4Phrasal Verbs and Idioms 978 0 7136 7805 5TOEFL 978 0 7136 8414 8TOEIC 978 0 7136 7508 5

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DICTIONARY OFSCIENCE ANDTECHNOLOGY

Simon Collin

second edition

A & C Black London

First edition published in 2003 byBloomsbury Publishing Plc.

This second edition published 2007 byA&C Black Publishers Ltd

38 Soho Square, London W1D 3HB

Copyright A&C Black 2007

All rights reserved. No part of this publication may be reproduced in any formor by any means without the prior written permission of the publishers.

A CIP record for this book is available from the British Library.

ISBN: 978 0 7136 8651 7

Text Production and ProofreadingJoel Adams, Sandra Anderson, Heather Bateman, Emma Djonokusumo,

Ruth Hillmore, Daisy Jackson, Irene Lakhani, Sarah Lusznat,Katy McAdam

This book is produced using paper that is made from wood grown in managed,sustainable forests. It is natural, renewable and recyclable. The logging andmanufacturing processes conform to the environmental regulations of the

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Text processed and typeset by A&C BlackPrinted in Spain by GraphyCems

PrefaceThis dictionary provides a wide range of vocabulary drawn from acrossthe fields of science and technology, including chemistry, physics andbiology, earth sciences, engineering, astronomy, electronics, medicineand telecommunications.

This fully up-to-date second edition gives clear and concise definitionsfor hundreds of new terms, from fast-moving fields such asbiotechnology, computing and environmental science. Its an idealreference for students, or anyone dealing with scientific or technicallanguage.

Thanks are due to the following people for their valuable comments andadvice on the first edition of the text: Lesley Brown, Judith Cheney, ClareConboy, Rich Cutler, Lynn Davy, Susan Jellis, Geoffrey Priddle andCharlotte Regan.

SUBJECT LABELS USED IN THE DICTIONARY OF SCIENCEAND TECHNOLOGY

ACOUSTICS AcousticsAEROSP AerospaceAGRIC AgricultureANAT AnatomyANTHROP AnthropologyARCHAEOL ArchaeologyASTRON AstronomyAUTOMOT AutomotiveAVIAT AviationBIOCHEM BiochemistryBIOL BiologyBIOTECH BiotechnologyBIRDS BirdsBOT BotanyCHEM ChemistryCHEM ELEM Chemical elementsCOMPUT ComputingCONSTR ConstructionCRYSTALS CrystalsDENT DentistryEARTH SCI Earth scienceECOL EcologyELEC ElectricityELEC ENG Electrical

engineeringELECTRONICS ElectronicsENG EngineeringENVIRON EnvironmentFISH FishFISHERIES FisheriesFOOD FoodFOOD INDUST Food industryFORESTRY ForestryFUNGI FungiGENETICS GeneticsGEOG GeographyGEOL GeologyHEALTH HealthIMMUNOL ImmunologyINDUST Industry

INSECTS InsectsLOGIC LogicMANUF ManufacturingMARINE BIOL Marine biologyMATHS MathematicsMEASURE MeasurementsMECH ENG Mechanical

engineeringMED MedicineMEDIA MediaMETALL MetallurgyMETEOROL MeteorologyMICROBIOL MicrobiologyMINERALS MineralsNAUT NauticalNAVIG NavigationOCEANOG OceanographyONLINE OnlineOPHTHALMOL OphthalmologyOPTICS OpticsPALAEONT PalaeontologyPHARM PharmacologyPHOTOGRAPHY PhotographyPHYS PhysicsPHYSIOL PhysiologyPLANTS PlantsPRINTING PrintingPSYCHIAT PsychiatryPSYCHOL PsychologySCI ScienceSOC SCI Social sciencesSTATS StatisticsTECH TechnologyTELECOM TelecommunicationsTEXTILES TextilesTIME TimeTRANSP TransportTREES TreesVET Veterinary medicineZOOL Zoology

AA1 symbol 1. MATHS the hexadecimalequivalent of the decimal number 10 2.MEASURE, ELEC ampereA2 noun ASTRON a class of stars with a sur-face temperature of 750010000C, andstrong spectral lines due to hydrogen.Examples include Sirius, Deneb, Vega andother bright stars. (NOTE: A stars tend to bewhite or bluish in colour. Apparent in thespectra of A stars are ionised metals likemagnesium and calcium.)A: noun COMPUT (in some operating sys-tems) the first disk drive on the system Tosee what is stored on your floppy disk, usethe DOS command DIR A:.ab- prefix away fromabandon verb COMPUT to clear a docu-ment, file or work from the computersmemory without saving it to disk or tape Once you have abandoned your spread-sheet, you cannot retrieve it again.abate verb to become less strong orintense The wind has abated.abatement noun a reduction in strengthor intensity water pollution abatementabbreviate verb to shorten a word or atext

abbreviated address noun COMPUT ausername that has fewer characters thanthe full name, making it easier to remem-ber or type inabbreviation noun the short form of awordabdomen noun ANAT 1. (in a vertebrate)a space in the body situated below orbehind the diaphragm and above or in frontof the pelvis, containing the stomach,intestines, liver and other vital organs 2. (inan arthropod) the rear section of the body

abdominal aorta noun ANAT the part ofthe aorta between the diaphragm and thepoint where it divides into the iliac arteries

abducent nerve noun ANAT the sixthcranial nerve which controls the musclewhich makes the eyeball turnabduct verb PHYSIOL to pull away fromthe centre line of the body. Oppositeadductabductor noun ANAT a muscle that pullsthe body or a limb away from a midpoint ormidlineabend noun COMPUT an unexpected stop-page of a program that is being run, due toa fault, error or power failure An inter-rupt from a faulty printer caused an abend.Full form abnormal endaberrant adjective not usual or typicalaberration noun 1. something which isnot usual or typical 2. a distortion of a tel-evision picture caused by a corrupt signalor incorrect adjustment 3. ASTRON the dif-ference between the observed and the cal-culated position of an astronomical body,caused by the time taken for light or otherradiation to travel from it to the observer 4.OPTICS the imperfect formation of animage by a telescope or other opticalinstrument

COMMENT: Varieties of optical aberrationinclude chromatic aberration, the differen-tial focusing of light of different wave-lengths, and spherical aberration, theimperfect focusing of light because of theuse of a spherical rather than a paraboliclens or mirror surface.

abiogenesis noun BIOL the theory thatlife can arise from nonliving materialsabiotic adjective BIOL not relating to a liv-ing organism abiotic factors

abiotic factor noun something whichinfluences the environment but which isnot produced by living organisms, e.g.wind, temperature or rainfall. Comparebiotic factor

abiotic stress noun stress caused byenvironmental factors such as drought or

abiotic stress resistance 2extreme heat or cold, not by biological fac-tors

abiotic stress resistance nounresistance in organisms to stress arisingfrom non-biological causes such asdrought or salinityablation noun 1. the removal of the toplayer of something 2. MED the removal of alayer of tissue by surgery 3. COMPUT amethod of writing data to an optical stor-age device, by which a laser burns a hole orpit representing digital bits of data into thesurface of the device 4. GEOL the removalof snow or ice from the surface of a glacierby melting or by the action of the wind

ablation zone noun GEOL a section of aglacier from which it loses snow or ice byablationabnormal adjective not usual or typical abnormal error Its abnormal for twoconsecutive disk drives to break down.

abnormal end noun COMPUT full formof abendabnormality noun a form or actionwhich is not usual or typicalabnormally adverb not as usual Thesignal is abnormally weak. The errorrate is abnormally high.

abnormal weather conditions pluralnoun METEOROL unusual or unfavourableweather conditionsabort verb 1. to stop a process or thedevelopment of something before it is fin-ished, or to stop developing Weather con-ditions forced them to abort the test flight.2. MED to end a pregnancy in a woman oranimal and prevent the birth of a child oryoung 3. BIOL to give birth before the usualend of a pregnancy (technical) Also calledmiscarry 4. COMPUT to end a process whena malfunction occurs by switching thecomputer off manually or by an internalfeature The program was aborted bypressing the red button.abortion noun MED a situation where anunborn baby leaves the uterus before theend of pregnancy, especially during thefirst 28 weeks of pregnancy when it is notlikely to survive birth (technical) to havean abortion BIOL to have an operation toend a pregnancy in order not to have a child

abort sequence noun COMPUT a uniquesequence of bits that indicates that thetransmission will be abnormally termi-nated. reset

ABO system noun MED a system of clas-sifying blood groupsabove preposition, adverb higher or morethan 2000 metres above sea level Thetemperature was above 40C for severalweeks. The occurrence of matching pairswas 70% or above. All the results areabove average.ABR abbreviation COMPUT available bitrateabrasion noun 1. MED a condition wherethe surface of the skin has been rubbed offby a rough surface and bleeds 2. EARTH SCIthe wearing away by friction of a material,especially the erosion of rock by the actionof particles suspended in water, ice or windABS noun COMPUT a programminginstruction that returns the magnitude of anumber without the numbers sign Thecommand ABS(-13) will return the answer13. Full form absolute functionabscess noun MED a painful swollenarea where pus forms

abscisic acid noun BIOCHEM a planthormone which is involved in seed forma-tion and in the closure of leaf pores duringdrought (NOTE: It was originally thought topromote leaf fall, but its importance in thisis now doubtful.)abscission noun BOT the shedding of aleaf or fruit due to the formation of a layerof cells between the leaf or fruit and therest of the plant (NOTE: It occurs naturally inautumn, e.g. leaf fall, or at any time of theyear in response to stress.)absence noun the fact of not beingpresent in the absence of because some-thing is not present in the absence of anyother symptomsabsent adjective not present Normalsymptoms of malaria are absent in thisform of the disease.absolute adjective 1. complete or total No absolute correlation with climatechange has yet been established. 2. meas-ured relative to a standard noun anunchanging principle

absolute address noun COMPUT 1. acomputer storage address that directly,without any modification, accesses a loca-tion or device Program execution isslightly faster if you code only with abso-lute addresses. Compare indexedaddress. Also called actual address,machine address 2. a computer storageaddress that can only access one location

3 absorption spectrum

absolute alcohol noun CHEM alcoholwhich contains no water

absolute assembler noun COMPUT atype of assembly language programdesigned to produce code which uses onlyabsolute addresses and values

absolute code noun COMPUT a binarycode which directly operates the centralprocessing unit, using only absoluteaddresses and values. object code (NOTE:This is the final form of a program after acompiler or assembler pass.)

absolute coordinate noun MATHS oneof the coordinates that describe the dis-tance of a point from the intersection ofaxes. Compare relative coordinate

absolute function noun COMPUT fullform of ABS

absolute humidity noun PHYS the massof water vapour in a given quantity of air

absolute loader noun COMPUT a pro-gram that loads a section of code into themain memory. Compare bootstrap loader

absolute magnitude noun ASTRON themagnitude of a star or other astronomicalobject, seen from a distance of 10 parsecs

COMMENT: The apparent magnitude ofastronomical objects seen from the Earthdepends upon their intrinsic brightness andalso upon how far away they are, so that theMoon can outshine everything else in thenight sky by being the nearest astronomicalobject. Comparing astronomical objects asthey would appear from a uniform distanceremoves this effect.

absolute pressure noun PHYS (of agas) a unit of force per unit of area withoutcomparison to other pressure Aircraftshow absolute pressure in inches of mer-cury on the inlet manifold pressure gauge.

absolute temperature noun PHYS thetemperature derived from the laws of ther-modynamics rather than based on the prop-erties of substances. Also calledthermodynamic temperature (NOTE: Itsunit is the kelvin.)

absolute time noun COMPUT the lengthof time that an audio disc has been playing

absolute value noun MATHS a size orvalue of a number regardless of its sign,e.g. the absolute value of 64.32 is 64.32

absolute zero noun PHYS the lowesttemperature possible, 0K or 273.15C(NOTE: Absolute zero is the condition ofhaving no thermal energy at all and is the-oretically impossible, although scientists

have managed to cool some materials tovery near it.)absorb verb 1. to take something in Theatmosphere absorbs radio waves. Warmair absorbs moisture more easily than coldair. Our bodies absorb oxygen. Saltabsorbs moisture from the air. 2. toabsorb information to take in and under-stand information There wasnt enoughtime to absorb the details of the reportbefore the meeting.absorbance noun PHYS same asabsorptanceabsorbent adjective able to absorb noun a substance or part of an organismsuch as a root tip which can take up some-thing such as moisture or nutrientsabsorptance noun PHYS a measure ofhow completely an object or substanceabsorbs radiant energy (NOTE: It equals theratio of the energy absorbed to the totalenergy falling on the object.)absorption noun 1. the process of takingin water, dissolved minerals and othernutrients across cell membranes There isabsorption of energy by the tyre when theaircraft lands. 2. PHYSIOL the taking intothe body of substances such as proteins orfats which have been digested from foodand enter the bloodstream from the stom-ach and intestines 3. CHEM the taking up ofone type of substance by another, e.g. of aliquid by a solid or of a gas by a liquid 4.COMPUT the power loss of a signal whentravelling through a medium, due to itsabsorptance

absorption filter noun PHYS a filter thatblocks specific colours of light

absorption line noun ASTRON a darkline seen in a stellar spectrum, caused byradiation passing through a cool mediumon its journey to the observer (NOTE:Absorption lines give information aboutcool matter such as interstellar gas clouds,planetary atmospheres and stellar atmos-pheres.)

absorption plant noun INDUST a part ofa petroleum processing plant, where oil isextracted from natural gas

absorption rate noun PHYS the rate atwhich a liquid is absorbed by a solid

absorption spectrum noun PHYS thepattern of dark bands seen when electro-magnetic radiation passes through anabsorbing medium and is observed with aspectroscope (NOTE: It results from some

absorptive capacity 4frequencies of the radiation beingabsorbed more completely than others.Different substances absorb at differentfrequencies and hence produce character-istic absorption spectra that can be used toidentify them.)

absorptive capacity noun BIOL theability of a substance or part of an organ-ism to take up something such as moistureor nutrientsabsorptivity noun PHYS same asabsorptanceabstract noun a short summary of a doc-ument Its quicker to search through theabstracts than the full text. verb 1. ENVI-RON to remove water from a river so that itcan be used by industry, farmers or garden-ers 2. EARTH SCI to take something such asgas, oil, mineral resources or gravel fromthe ground

abstract data type noun COMPUT ageneral data type that can store any kind ofinformation The stack is a structure ofabstract data types which can store anytype of data from an integer to an address.abstraction noun 1. ENVIRON theremoval of water from a river or othersource for use by industry, farmers or gar-deners 2. EARTH SCI the removal of some-thing such as gas, oil, mineral resources orgravel from the groundabundance noun 1. a large amount ornumber of something The area supportsan abundance of wildlife. 2. a measure ofquantity applied to plants or animals, oftenbased on density or frequency 3. ASTRONthe relative amount of a particular type ofstar, galaxy, atom or other item in an over-all populationabundant adjective occurring or availa-ble in large quantities a region of abun-dant rainfall The ocean has an abundantsupply of krill.abyss noun EARTH SCI a very deep part ofthe seaabyssal adjective EARTH SCI referring tothe deepest part of the sea

abyssal plain noun EARTH SCI a flat partof the seabed at the deepest level, approxi-mately 4000m below sea level

abyssal zone noun EARTH SCI a deepand dark part of the sea below the euphoticzone, at its deepest about 6000m deep,where light cannot reach and plant and ani-mal life is rare (NOTE: The deepest part ofthe sea is the hadal zone)

abyssobenthic adjective MARINE BIOLreferring to an organism living on the floorof the deepest part of a sea or lakeabyssopelagic adjective MARINE BIOLreferring to an organism living in the deep-est part of a sea or lake, at depths greaterthan 3000mAc symbol CHEM ELEM actiniumAC1 abbreviation ELEC alternating currentAC2 abbreviation METEOROL altocumulusacaricide noun BIOL a substance used tokill mites and ticksacarid noun BIOL a small animal whichfeeds on plants or other animals by pierc-ing the outer skin and sucking juices, e.g. amite or tickAcarida noun ZOOL the order of animalsincluding mites and ticksacaridicide noun BIOL same as acari-cideAcarina noun ZOOL same as AcaridaACC noun COMPUT the most importantinternal CPU storage register, containingthe result of an operation or the data wordwhich is to be processed. Full form accu-mulatoraccelerate verb to increase in speed After start-up, the engine accelerates up toidling speed. The aircraft accelerateddown the runway and took off. Oppositedecelerate

accelerated graphics port nounCOMPUT an interface in a computerbetween a graphics controller and themotherboard that transfers data veryquickly, providing high-performancethree-dimensional graphics and videoprocessing capabilities. Abbr AGP (NOTE:This port does not replace a PCI bus butworks with it.)acceleration noun 1. the act of acceler-ating Acceleration can be felt as the air-craft begins its take-off run. accelerationdue to gravity acceleration of an objectdue to the gravitational attraction of theEarth, with a standard value of9.80665ms-2. Symbol g 2. PHYS the rate ofchange of velocity. Opposite deceleration3. an outward force caused by change indirection without changing speed Accel-eration forces can be felt during aerobaticmanoeuvres.

COMMENT: The SI units of acceleration arems-2 metres per second per second. Theformula to calculate acceleration is a = (v u)/t where a = acceleration, v = final

5 access linevelocity, u = starting velocity and t = timetaken.

acceleration time noun COMPUT 1. thetime taken for a disk drive to spin a disk atthe correct speed, from rest Allow foracceleration time in the access time. 2. thetotal time between an access instructionbeing issued to a peripheral and the databeing transferredaccelerator noun 1. ENG a machinewhich changes the velocity of an objectand so increases its kinetic energy 2. CHEMa substance which changes the speed atwhich a chemical reaction takes place

accelerator board, accelerator cardnoun COMPUT a circuit board which carriesa faster or more advanced version of thesame processor that runs a computer, ena-bling the computer to run faster

accelerator key noun COMPUT a combi-nation of keys which, when pressedtogether, carry out a function that wouldotherwise have to be selected from a menuusing a mouse. For example, instead ofselecting the File menu then the Saveoption, using the accelerator keys Alt and Sdoes the same thing.accentuate verb to make somethingstronger Moving accentuated the pain.accept verb 1. to take or receive some-thing which is offered 2. to be able to takeor receive something Some units acceptelectrical inputs from the autopilot. 3. toaccept responsibility to be willing to beanswerable for something The depart-ment accepted responsibility for the inci-dent. 4. COMPUT to establish a session orconnection with another deviceacceptable adjective allowable orapproved of, although it may not be perfect The error rate was very low and isacceptable. There must be a continuousflow of clean oil at an acceptable tempera-ture. acceptable limits generally agreedstandards or restrictions within a range ofmaximum and minimum figures

acceptable daily intake noun BIOL thequantity of a substance such as a nutrient,vitamin, additive or pollutant which a per-son or animal can safely consume dailyover their lifetime. Abbr ADI

acceptable use policy noun COMPUTa set of rules which describe what a usercan write or do on the Internet withoutoffending other users. Abbr AUPacceptance noun 1. a willingness tobelieve something There is a growing

acceptance that safety is the main priority.2. a willingness to do or use something acceptance of new technology

acceptance angle noun OPTICS theangle of total field of view of a lens or fibreoptic

acceptance sampling noun INDUSTthe testing of a small random part of abatch to see if the whole batch is up tostandard

access arm noun COMPUT a mechanicaldevice in a disk drive, used to position theread/write head over the correct track on adisk The access arm moves to the park-ing region during transport.

access code noun COMPUT a series ofcharacters or symbols which must beentered to identify a user before access to acomputer is permitted. password

access control noun COMPUT a securitydevice such as a password which onlyallows selected users to use a computersystem or read files

access control list noun COMPUT asecurity system which has usernames andpasswords checked by the operating sys-tem to find out if a specific user is allowedaccess to a resource or feature of a networkor shared computer. Abbr ACL

access head noun COMPUT a part of adisk drive which moves to the correct partof the disks surface and reads informationstored on the diskaccessibility noun the ease with whichsomething can be reached or found Accessibility of components and equip-ment during servicing enables work to bedone more quickly.accessible adjective easy to reach orfind Instruments which need resetting inflight must be accessible to the crew. Details of customers are easily accessiblefrom the main computer files.

accession number noun COMPUT anumber in a record that shows in whichorder each record was entered

access level noun COMPUT a predefinedaccess category for users of a computer orsystem. The lowest access level mightallow the user to only view data, while thehighest access level allows a user to doanything.

access line noun COMPUT a perma-nently connected communications linebetween a terminal and a computer

access log 6 access log noun COMPUT a file on a

website server computer that contains arecord of every visitor to the website,showing when a person visited and whichpages were viewed The access log isinvaluable we produce graphs of thepages that are most popular using anaccess log analyser program. He ana-lysed the access log to see if their compet-itor had visited their website.

access method noun COMPUT 1. themeans used for the internal transfer of databetween a computers memory and displayor peripheral devices (NOTE: Differences inthe methods used are often the cause ofcompatibility problems.) 2. a set of rulesthat allows a device to send data onto a net-work (NOTE: Token passing and CSMA/CDare two methods commonly used in a localarea network.)

access name noun COMPUT a uniquename that identifies an object in a databaseaccessor noun COMPUT a person whoaccesses dataaccessory noun a system or piece ofequipment of secondary importance acamera with several accessories The spe-cial offer includes a range of accessoriesincluding a mouse and modem. adjectiveof secondary importance There are manyaccessory systems which need enginepower to operate them, e.g. pumps, gener-ators and magnetos.

accessory nerve noun ANAT the elev-enth cranial nerve, which supplies the mus-cles in the neck and shoulders

access path noun COMPUT a descriptionof the location of a stored file within adirectory structure of a disk

access period noun COMPUT a periodof time during which a user can access data

access permission noun COMPUT adescription of all the access rights for aparticular user

access point noun COMPUT a test pointon a circuit board or in software, allowingan engineer to check signals or data

access provider noun COMPUT Inter-net service provider

access rights plural noun COMPUT per-mission for a specific user to access a par-ticular file or data object

access time noun COMPUT 1. the totaltime which a storage device takes betweenthe data being requested and returned The access time of this dynamic RAM chip

is around 200nS we have faster versionsif your system clock is running faster. 2. thelength of time required to find a file or pro-gram, either in the main memory or a sec-ondary memory source 3. the time taken tofind and retrieve a particular piece of datafrom memory or a hard diskaccident noun an unfortunate or harmfulevent Accidents must be reported. Thelab assistant was injured in the accident. by accident without being plannedaccidental adjective 1. not deliberate orintentional Always keep backup copies incase of accidental damage to the masterfile. 2. referring to an accident We weretold of his accidental death.

accident prevention noun the estab-lishing of procedures to stop accidentshappeningacclimatisation, acclimatization,acclimation noun BIOL the process ofadapting to a different environment (NOTE:This process is known as acclimatisationif the changes occur naturally and accli-mation if they are produced in laboratoryconditions.)acclimatise, acclimatize verb BIOL 1. tomake an organism become used to a differ-ent environment, usually a change in cli-mate 2. to become used to a different sortof environment

COMMENT: When an organism such as aplant or animal is acclimatising, it isadapting physically to different environ-mental conditions, such as changes in foodsupply, temperature or altitude.

accommodation noun PHYSIOL theability of the lens of the eye to focus onobjects at different distances, using the cil-iary muscle

accommodation reflex noun PHYSIOLa reaction of the pupil when the eyefocuses on an object which is closeaccomplishment noun PHYS workdone Power is measured by units ofaccomplishment correlated with time.accordance noun in accordance withfollowing something such as rules, instruc-tions or laws Fuels must be used inaccordance with instructions.accordingly adverb as needed Checkfor increasing manifold pressure andreduce power accordingly.

according to preposition 1. in relationto The force exerted will vary accordingto a number of factors. 2. as written or saidby somebody else According to the

7 aceticco-pilot, engine vibration was detected inengine number one. according toinstructions exactly as said in the instruc-tions according to requirements asrequiredaccount noun 1. a spoken or writtenreport about something We gave a briefaccount of our experimental procedures. 2.COMPUT a record of a users name, pass-word and rights to access a network oronline system If you are a new user, youwill have to ask the supervisor to create anaccount for you. to take something intoaccount COMPUT to consider somethingcarefully When planning a flight, windspeed and direction must be taken intoaccount.

account for verb 1. to constitute some-thing Kevlar and carbon fibre accountfor a large percentage of the materialsused in modern aircraft. 2. to provide themain reason for something High humid-ity accounted for the difference betweenthe two results.

account name noun COMPUT theunique name of a user on a network oronline system John Smiths accountname is JSMITH.accrete verb to increase in amount byslow external addition Ice accretes on therotor.accretion noun 1. EARTH SCI the growthof inorganic objects by the attachment ofmaterial to their surface 2. BIOL the growthof a substance around an object an accre-tion of calcium round the joint 3. EARTHSCI an accumulation of sediments 4.ASTRON the accumulation of a number ofobjects to form a single larger one (NOTE: Itis thought that the planets, including theEarth, were built up by the accretion ofplanetesimals which formed a cloudaround the Sun almost five billion yearsago.)accumulate verb 1. to collect andincrease Cold air flows downwards andaccumulates over low ground. Largequantities of fat accumulated in the arter-ies. Sediment and debris accumulate atthe bottom of a lake. 2. to gather severalthings together over a period of time Wehave gradually accumulated a large col-lection of plant specimens.

accumulated temperature nounAGRIC the number of hours during whichthe temperature is above a particular point,taken as the minimum temperature neces-

sary for growing a specific crop (NOTE: Inthe UK, this is usually taken to be thenumber of hours above 6C.)accumulation noun 1. the process ofbecoming greater in size or quantity over aperiod of time the risk of accumulation oftoxins in the food chain 2. something thathas accumulated

accumulation zone noun GEOL a sec-tion of a glaciers movement downstreamduring which it increases in massaccumulator noun INDUST a device forstoring energy (NOTE: A rechargeable elec-tric cell is an accumulator.)accuracy noun 1. the state of being cor-rect to check for accuracy to make cer-tain that information or results are correct2. precision The accuracy of modernnavigational equipment is much greaterthan older systems. 3. COMPUT the totalnumber of bits used to define a number ina computer (NOTE: The more bits that areallocated the more accurate the definitionof the number is.)accurate adjective 1. correct Skill inaccurate flying can only be achieved bypractice. The printed bar code has to beaccurate to within a thousandth of amicron. The results of the lab tests shouldhelp the consultant make an accurate diag-nosis. 2. precise This watch is very accu-rate.accurately adverb with no errors TheOCR had difficulty in reading the new fontaccurately. The mistake occurredbecause the data had not been accuratelykeyed.acellular adjective referring to an organ-ism that is not made up of separate cellsacentric adjective GENETICS referring toa chromosome that lacks the structure atwhich the two arms of a chromosome join(centromere)acer noun TREES a maple or sycamoretree. Genus: Acer.acetaldehyde noun CHEM a colourlessvolatile liquid with an unpleasant smell.Formula: CH3CHO.acetamide noun CHEM a white crystal-line solid with moisture-absorbing proper-ties, used in the manufacture of organicchemicals. Formula: CH3CONH2.acetate noun CHEM a salt or ester of ace-tic acidacetic adjective CHEM containing a prod-uct of vinegar or acetic acid

acetic acid 8 acetic acid noun CHEM a colourless

hygroscopic acid with a sharp smell that isthe main component of vinegar. Formula:CH3COOH.acetone noun CHEM a colourless liquidthat has a sweetish smell and is flammable,used as a solvent and in the manufacture oforganic chemicals. It is formed in the bodyafter vomiting or as a result of diabetes.Formula: CH3COCH3.acetylcholine noun BIOCHEM a sub-stance that is released from the ends ofsome nerve fibres to transmit impulses toother nerve cells or to muscles. Formula:C7H17NO3.

acetyle chloride noun CHEM a colour-less liquid with a strong unpleasant smell,used to introduce the organic group CH3-into compoundsacetylene noun CHEM a colourlesshydrocarbon gas that is highly flammable,used in welding and the manufacture oforganic chemicals. Formula: C2H2.acetylide noun CHEM a potentially explo-sive compound of acetylene containing ametal ion

acetylsalicylic acid noun PHARM thechemical name for the drug aspirinachene noun BOT a dry single-seededfruit that does not split open (NOTE:Achenes are produced by plants such asdandelions and sunflowers.)achieve verb to succeed in doing or hav-ing something In order to achieve anacceptable result the experiment must bereplicated.achievement noun the successful com-pletion of something demanding Fortrainee pilots, the first solo flight is a greatachievement.achromatic adjective OPTICS referringto an optical device that has been correctedfor chromatic aberration

achromatic colour noun OPTICS col-our within the range between black andwhite displayed by a graphics adapter, or ashade of grey

achromatic lens noun OPTICS a lens inwhich two or more lenses with differentproperties are combined to prevent distor-tionACIA noun COMPUT a circuit that allows acomputer to transmit and receive serialdata using asynchronous access. Full formasynchronous communications inter-face adapter

acid noun CHEM 1. a chemical compoundcontaining hydrogen which dissolves inwater and forms hydrogen ions, or reactswith an alkali to form a salt and water, andturns litmus paper red 2. any bitter juice

acid deposition noun ENVIRON same asacid rain

acid fallout noun an acid which forms inthe atmosphere and falls as particles, with-out any water

acid grassland noun ECOL a type ofvegetation that typically grows on soilsthat drain freely and are low in mineralnutrients, and may also occur onpost-industrial sites. The range of plantspecies found is small. calcareousgrasslandacidic adjective CHEM containing or hav-ing the properties of an acid

acidic rock noun EARTH SCI a rockwhich contains a high percentage of silica

acidic solution noun CHEM a solutionwith a pH of less than 7 (NOTE: It is usuallya solution which has water as the solvent.)

acidic water noun CHEM water whichcontains acidacidification noun CHEM the process ofbecoming acid or of making a substancemore acid Acidification of the soil leadsto the destruction of some living organ-isms.acidify verb CHEM to make a substancemore acid, or to become more acid Acidrain acidifies the soils and waters where itfalls. The sulfur released from wetlandsas sulfate causes lakes to acidify.

acidifying compound noun a com-pound that contributes to acidification, e.g.sulfur oxides, sulfates, nitrogen oxides,nitrates and ammonium compoundsacidity noun 1. CHEM the proportion ofacid in a substance The alkaline solutionmay help to reduce acidity. 2. MED a formof indigestion where the patient has a burn-ing feeling in the stomach caused by toomuch acid forming there

COMMENT: Acidity and alkalinity are meas-ured according to the pH scale. pH7 isneutral. Numbers above pH7 show alka-linity, while those below show acidity.

acid-neutralising capacity nounCHEM the ability of water to neutraliseacids, measured by the amount of bicarbo-nate it contains. Abbr ANCacidosis noun MED an unusually highproportion of acid waste products such as

9 acrosomeurea in the blood, sometimes caused by ametabolic dysfunction (NOTE: As acidityincreases the rumen wall becomesinflamed. The animal dehydrates progres-sively, the blood turns more acidic and inextreme cases the animal may die.)

acid precipitation noun ENVIRON sameas acid rainacid-proof adjective CHEM able to resistthe harmful effects of an acid

acid pulse noun a sudden increase inacidity in rainwater or river water

acid rain noun ENVIRON precipitationsuch as rain or snow which contains ahigher level of acid than normal

COMMENT: Acid rain is mainly caused bysulfur dioxide, nitrogen oxide and otherpollutants being released into the atmos-phere when fossil fuels such as oil or coalcontaining sulfur are burnt. Carboncombines with sulfur trioxide fromsulfur-rich fuel to form particles of an acidsubstance. The effects of acid rain areprimarily felt by wildlife. The water in lakesbecomes very clear as fish and microscopicanimal life are killed. It is believed acid rainkills trees, especially conifers, making themgradually lose their leaves and die. Acidrain can also damage surfaces such as thestone surfaces of buildings when it falls onthem.

acid soot noun ENVIRON acid carbon par-ticles which fall from smoke from chim-neysACK noun COMPUT a signal that is sentfrom a receiver to indicate that a transmit-ted message has been received and that it isready for the next one The printer gener-ates an ACK signal when it has receiveddata. Full form acknowledge

Ackermans function noun COMPUT arecursive function used to test the ability ofa compiler to cope with recursionacknowledge COMPUT noun a signalthat is sent from a receiver to indicate thata transmitted message has been receivedand that it is ready for the next one verb1. to tell the person who sent somethingthat it has been received 2. to send a signalfrom a receiver to show that a transmittedmessage has been received

acknowledge character noun COM-PUT a special code sent by a receiver toindicate to the transmitter that a messagehas been correctly receivedACL abbreviation COMPUT access controllistacorn noun BOT the fruit of an oak tree

acoustic adjective referring to sound acoustic feedback adjective ACOUS-

TICS feedbackacoustician noun ACOUSTICS a personwho specialises in the study of sound

acoustic nerve noun ANAT the eighthcranial nerve, which governs hearing andbalanceacoustics noun ACOUSTICS the study ofsound, especially noise levels in buildingsACPI noun COMPUT a part of the Micro-soft Windows 98 software system thatallows the operating system to automati-cally configure compatible hardware. Fullform advanced configuration and powerinterface

acqua regia noun CHEM a solution thatcan dissolve metals, made up of one partnitric acid and three parts hydrochloricacidacquired adjective BIOL not inherited butdeveloped in response to the environment

acquired character noun BIOL a char-acteristic that develops in response to theenvironment

acquired immunity noun MED immu-nity which is not inherited but has devel-oped in response to infection orinoculationACR abbreviation audio cassette recorderacre noun AGRIC, MEASURE a unit ofmeasurement of land area, equal to 4840square yards or 0.4047 hectaresACRE abbreviation Advisory Committeeon Releases to the Environmentacreage noun AGRIC, MEASURE the areaof a piece of land measured in acresacrid adjective having a strong bittersmell or taste acrid fumesacro- prefix BIOL referring to a point or tipacrocentric adjective GENETICS refer-ring to a chromosome that has arms of une-qual length, because the structure at whichthe two arms join (centromere) is locatednear one endacrolein noun CHEM a poisonousstrong-smelling liquid used in the produc-tion of resins and medicinesacronym noun a word which is made upof the initial letters of several words and ispronounced as a word NASA is the acro-nym for National Aeronautics and SpaceAdministration.acrosome noun BIOL a sac or cap at thefront of a sperm cell that releases enzymes

acrylic acid 10to digest the egg coats enabling the spermto penetrate the egg

acrylic acid noun CHEM a colourlessacid with corrosive properties, used in themanufacture of acrylate resin. Formula:CH2CHCO2H.

acrylic fibre noun CHEM a synthetic tex-tile fibre made from acrylonitrileacrylonitrile noun CHEM a colourlesstoxic liquid which is moderately volatile,used in the manufacture of acrylic fibre,resin, rubber and thermoplastics. Formula:CH2CHCN.ACS noun COMPUT a server that sendsdata in one direction, one character at atime. Full form asynchronous communi-cation serveract verb 1. to behave in a particular way The crew must act with authority. 2. to takeon a role Mountain ranges act as a bar-rier. The governor spill valve also acts asa safety relief valve. 3. to produce an effect Gravity acts vertically downwards.ACTH noun BIOCHEM a hormone whichstimulates the adrenal glands to producesteroid hormones. Full form adrenocorti-cotrophic hormoneactin noun BIOCHEM a protein which, withmyosin, forms the contractile tissue ofmuscle

actinic radiation noun PHYS a type ofradiation which can cause a chemical reac-tionactinide noun CHEM ELEM one of the radi-oactive elements which are in the same cat-egory as uranium in the periodic table andhave atomic numbers from 89 to 104

COMMENT: Actinides are waste productsfrom nuclear fission. They pose problemsfor disposal as some of them have very longhalf-lives. They can be reduced to moredisposable forms by burning in fast reac-tors.

actinium noun CHEM ELEM a natural radi-oactive element, produced by the decay ofuranium-235 (NOTE: The chemical symbolis Ac; the atomic number is 89 and theatomic weight is 226.)actinomycete noun MICROBIOL a bacte-rium shaped like a rod or filament. Order:Actinomycetales. (NOTE: Some actinomyc-etes cause diseases while others aresources of antibiotics.)action noun 1. something done or to bedone Appropriate action should be takento avoid contamination. 2. the effect thatsomething has worn away by the action

of rain the action of the drug on the nerv-ous system 3. COMPUT something that hap-pens when the user does something, e.g.presses a special key that moves the cursorto the action bar at the top of the screen

action bar noun COMPUT the top line ofthe screen that displays the menu names

action code noun COMPUT a single letterassociated with a specific menu option tospeed up selection so that when the letter ispressed the menu option is selectedaction-object noun COMPUT an object towhich a user specifies that an action shouldbe applied

action plan noun a detailed statement ofhow something that needs to be done willbe carried out an action plan for conserv-ing species

action potential noun PHYSIOL a transi-tory alteration in electrical potential occur-ring between the inside and the outside ofa nerve or muscle fibre, caused by trans-mission of a nerve impulseactivate verb 1. to start a process or tomake something start working PressingCR activates the printer. 2. COMPUT (in anauthoring tool or programming language)to make a button or menu option or field ona screen layout available to a user If thebutton or field is not activated, it is nor-mally displayed greyed out and does notrespond if a user selects it.

activated carbon, activated charcoalnoun CHEM a form of carbon to whichgases can stick, used in filters or added towater as it is being treated before domesticconsumption

activated sludge noun ENVIRON solidsewage containing active microorganismsand air, mixed with untreated sewage tospeed up the purification processactivation noun the act of making some-thing start to work

activation energy noun CHEM theamount of energy required to start a chem-ical reaction by breaking a chemical bondactivator noun CHEM a substance whichactivates a process a compost activatoractive adjective 1. doing something, usu-ally energetically, or being alert Kiwisare only active after dark. Mental exer-cises keep the mind active and alert. 2. inaction or in use the system is active thesystem is on and working 3. not passive in a secondary radar system, the targetis active in a secondary radar system the

11 activitytarget transmits a signal 4. COMPUT busy,working or being used 5. MED (of disease)not dormant after two years of activerheumatoid disease 6. EARTH SCI (of a vol-cano) likely to erupt from time to time

active application noun COMPUT anapplication currently being used by a user

active Cb cloud noun METEOROL acumulonimbus cloud that is developing

active file noun COMPUT a computer filewhich is being worked on

active galactic nucleus noun ASTRONa zone in the central region of some galax-ies where a mass of up to 100 million timesthat of the Sun is concentrated, emittinglarge and variable amounts of radiation.Abbr AGN

active high noun ELECTRONICS an elec-tronic signal which is valid when it is highor logical one

active immunity noun the productionof antibodies by an animal or person as aresult of experiencing the disease organ-isms that cause the disease in question, orbeing vaccinated against it

active ingredient noun CHEM, PHARMthe main effective ingredient of somethingsuch as an ointment or agrochemical, asopposed to the base substance. Abbr AI

active line noun COMPUT a line in a com-munications link or port which is beingused to transfer data or carry control sig-nals

active link noun COMPUT the link cur-rently being used to transfer information

active low noun ELECTRONICS an elec-tronic signal which is valid when it is lowor logical zero

active margin noun EARTH SCI an areaat the edge of a continental mass wherevolcanic activity is frequent

active mass noun CHEM a concentrationof a substance which is part of a chemicalreaction

active matrix display noun COMPUT atype of colour display used in laptop com-puters (NOTE: normally called TFT display)

active organic matter noun BIOCHEMorganic matter in the process of being bro-ken down by bacteria. Abbr AOM

active packaging noun ENVIRON foodpackaging that interacts chemically or bio-logically with its contents so that shelf-lifeis longer or the product is modified duringstorage

active principle noun PHARM the mainmedicinal ingredient of a drug whichmakes it have the required effect on apatient

Active Server Page noun COMPUT awebpage that is created only whenaccessed by a visitor, allowing the websiteto display up-to-date information or infor-mation from a database The databasesearch results page is implemented as anActive Server Page. Abbr ASP

active site noun BIOCHEM the region ofan enzyme molecule where a substance(substrate) is bound and acted upon by theenzyme

active star noun COMPUT a network con-sisting of a central point with nodesbranching out, in which one central com-puter controls and routes all messagesbetween devices

active storage noun COMPUT afast-access RAM whose locations can bedirectly and immediately addressed by thecentral processing unit, used as main stor-age

Active Streaming Format noun COM-PUT a multimedia delivery format devel-oped by Microsoft for delivery over theInternet and used in its NetShow product.Abbr ASF

active transport noun BIOCHEM a trans-fer of substances across a cell membranefor which energy is required

active volcano noun EARTH SCI a vol-cano which is erupting, or likely to erupt

active window noun COMPUT 1. an areaof display screen in which a user is cur-rently working. window 2. the windowthat is currently the focus of cursor move-ments and screen displaysActiveX noun COMPUT a programminglanguage and program definition used tocreate small applications designed toenhance the functionality of a webpage

COMMENT: ActiveX applications, calledapplets, are often used to add database ormultimedia effects to a website that cannotbe supported with basic HTML commands.When a user visits the webpage that usesthe ActiveX applet, the program is automat-ically downloaded by the users browserand run on the users computer.

activity noun 1. the actions that humansand other living things undertake research activities The hillside showedsigns of human activity. We saw no activ-ity around the nest in several hours. 2. the

activity loading 12effect that something has Biopesticidesare being evaluated for their biologicalactivity in a range of environments. 3. anaction or movement volcanic activity 4.COMPUT being active or busy

activity loading noun COMPUT amethod of organising disk contents so thatthe most frequently accessed files or pro-grams can be loaded quickly

activity ratio noun COMPUT the numberof files currently in use compared to thetotal number stored

act on, act upon verb 1. (of force) to pro-duce an effect on something lBendingand twisting forces act on a propeller. The antibiotic acted quickly on the infec-tion. 2. act upon to do something as theresult of something which has been said He acted upon your suggestion.actual adjective real rather than expectedor guessed What are the actual figuresfor the number of students this year?

actual address noun COMPUT same asabsolute address

actual code noun COMPUT a binary codewhich directly operates the centralprocessing unit, using only absoluteaddresses and values (NOTE: This is thefinal form of a program after a compiler orassembler pass.)

actual instruction noun COMPUT theinstruction executed as a result of the mod-ification of an original instructionactually adverb in fact The design issuch that, although the aircraft loses alti-tude rapidly, it does not actually stall.actuate verb 1. to switch on or put intooperation a system or a piece of equipment A lever actuates the fire deluge system. The fore and aft movement of the controlcolumn actuates the elevators. 2. to put aprocedure into action Receipt of the dis-tress signal will actuate the emergencyprocedures.actuation noun the act of causing adevice or part to moveactuator noun 1. ENG a device whichchanges electrical or hydraulic energy intomechanical motion (NOTE: The actuator issensitive to engine rpm. Actuators areclassified as either linear or rotary.) 2. COM-PUT a mechanical device which can be con-trolled by an external signal, e.g. theread/write head in a disk driveACU noun COMPUT a device which allowsa computer to call stations or dial tele-

phone numbers automatically. Full formautomatic calling unitacuity noun 1. PHYSIOL the ability of theeye to define shades and shapes of anobject 2. BIOL the ability of the ear to detectfrequency or volume changesacute adjective 1. BIOL referring to a dis-ease which comes on rapidly and can bedangerous She had an acute attack ofshingles. Compare chronic 2. BIOL refer-ring to a pain which is sharp and intense acute chest pains Compare chronic 3.MATHS describes an angle that is less than90 4. MATHS describes a triangle that hasthree internal angles each of less than 90

acute exposure noun exposure to apollutant or radioactive substance for ashort period

acute health effect noun a health prob-lem which lasts a short time, followingexposure to a pollutant or radioactive sub-stance

acute toxicity noun MED the concentra-tion of a toxic substance which is highenough to make people seriously ill or cancause deathacyclic adjective BOT referring to flowerswhose parts are arranged in a spiral, not awhorl

acyl group noun CHEM a group of com-pounds with the basic chemical structureRCO-A/D abbreviation COMPUT analog to digitalADA noun COMPUT a high-level program-ming language that is used mainly in mili-tary, industrial and scientific fieldsadapt verb 1. to change to suit new condi-tions People adapt to the reducedamounts of oxygen available at high alti-tudes. 2. to change or modify somethingfor special use The engine has beenadapted to use the new fuel. 3. to experi-ence a heritable change in structure orfunction that makes an organism betterable to survive and reproduce, as part of theprocess of evolutionadaptability noun BIOL the ability of anorganism to change to fit a new situationadaptation noun 1. the act of changing,or of modifying something for special use Doppler VOR is an adaptation of VOR toreduce errors caused by location. 2. theadjustment to new conditions Adaptationto time changes when travelling west toeast needs time. Also called adaption 3.BIOL a heritable change in an organism so

13 add-inthat it is better able to survive and repro-duce in an environment, as part of the proc-ess of evolutionadapter, adaptor noun COMPUT a devicethat allows two or more incompatibledevices to be connected together Thecable adapter allows attachment of thescanner to the SCSI interface. The cableto connect the scanner to the adapter isincluded in the package.

adapter plug noun COMPUT a plugwhich allows devices with different typesof plug to be fitted into the same socketadaption noun same as adaptation

adaptive channel allocation nounCOMPUT the provision of communicationschannels according to demand rather thanas a fixed allocation

adaptive compression noun COMPUTa data compression system that continu-ously monitors the data it is compressingand adjusts its own algorithm to providethe most efficient compression

adaptive differential pulse codemodulation noun COMPUT a CCITTstandard that defines a method of convert-ing a voice or analog signal into a com-pressed digital signal. Abbr ADPCM

adaptive optics noun ASTRON an opti-cal system capable of adjusting to compen-sate for atmospheric distortion (NOTE:Adaptive optics was advanced during the1980s and 1990s because of spending bythe US on the Strategic Defense Initiative,which called for methods of firing laserbeams accurately through the atmos-phere. The method is now entering wideruse with big ground-based telescopessuch as the Keck telescope in Hawaii, fromwhich images matching in quality thosefrom the Hubble Space Telescope havebeen obtained.)

adaptive packet assembly nounCOMPUT a method used by the MNPerror-correcting protocol to adjust the sizeof data packets according to the quality ofthe telephone line. The better the line is,the bigger the packet size can be.

adaptive radiation noun BIOL thedevelopment of different species from asingle ancestor in such a way that the dif-ferent forms have adapted to suit differentenvironmental conditions

adaptive routing noun COMPUT theability of a system to change its communi-cations routes according to various events

or situations such as line failure (NOTE: Themessages are normally sent along themost cost-effective path unless there is aproblem with that route, in which case theyare automatically rerouted.)adaptor noun COMPUT another spellingof adapterADC noun COMPUT an electronic devicethat converts an analog input signal to adigital form that can be processed by acomputer. Full form analog to digitalconverteradd verb MATHS 1. to make a total fromsomething Add the two numbers togetherto find the sum. In the spreadsheet eachcolumn should be added to make a subto-tal. 2. to put together two or more things tomake a larger group or a group with differ-ent properties A substance is added to thefuel to clean fuel injectors. The softwarehouse has added a new management pack-age to its range of products. Adding ordeleting material from the text is easyusing function keys.addend noun MATHS a number added tothe augend in an additionadder noun COMPUT a device or routinethat provides the sum of two or more dig-ital or analog inputs full adder, threeinput adder a binary addition circuitwhich can produce the sum of two inputs,and can also accept a carry input, produc-ing a carry output if necessary halfadder a binary addition circuit which canproduce the sum of two inputs and a carryoutput if necessary, but will not accept acarry input

COMMENT: A parallel adder takes one clockcycle to add two words, while a serial addertakes a time equal to the number of bits in aword to add.

adder-subtractor noun COMPUT adevice that can either add or subtract

add file noun COMPUT a special file inwhich new records are stored prior toupdating the main databaseaddict noun MED a person who isaddicted to a harmful drugaddicted adjective BIOL physiologicallyor psychologically dependent on a harmfuldrugaddictive adjective BIOL referring to adrug which people can become addicted to Heroin is addictive.add-in COMPUT adjective added to a com-puter program or piece of equipment anadd-in processor card. Processing is

addition 14much faster with add-in cards. noun acomputer program or piece of equipmentwhich is added to anotheraddition noun 1. MATHS a mathematicaloperation which combines numbers Theaddition sign is +. Addition is normallytaught before subtraction, multiplicationand division. 2. CHEM addition reaction With the addition of methanol, the tur-bine inlet temperature is restored. 3.MATHS in addition also in addition toas well asadditional adjective COMPUT extra Canwe link three additional workstations to thenetwork?

addition reaction noun CHEM a chemi-cal reaction in which two substances com-bine to form a third substance with noby-products or other substances beingformed. Compare substitution reaction(NOTE: usually refers to reactions inorganic chemistry)

addition record noun COMPUT a recordwith changes used to update a masterrecord or file

addition sign noun MATHS a sign (+)used to show that numbers are added. Alsocalled plus sign

addition time noun COMPUT the time anadder takes to carry out an add operation

addition without carry noun COMPUTan addition operation without any carrybits or wordsadditive noun 1. FOOD INDUST a chemicalwhich is added to food to improve itsappearance or to keep it fresh The tin ofbeans contains a number of additives. These animal foodstuffs are free from alladditives. 2. CHEM a chemical which isadded to something to improve it A newfuel additive made from plants could helpreduce energy costs.

COMMENT: Colour additives are added tofood to improve its appearance. Some arenatural organic substances like saffron,carrot juice or caramel, but others aresynthetic. Other substances added to foodto prevent decay or to keep the food in theright form are emulsifiers, which binddifferent foods together as mixtures, andstabilisers, which can keep a saucesemi-liquid and prevent it from separatinginto solids and liquids. The European Unionallows some additives to be added to foodand these are given E numbers.

add-on COMPUT noun a piece of softwareor hardware that is added to a computersystem to improve its performance The

add-on will boost the computers storagecapabilities. The new add-on boardallows colour graphics to be displayed. adjective added to a computer system toimprove its performance opposite (allsenses) built-in

add register noun COMPUT a registerwhich is an adderaddress COMPUT noun 1. a numberallowing a central processing unit in acomputer system to reference a physicallocation in a storage medium Each sepa-rate memory word has its own uniqueaddress. 2. a unique number that identifiesa device on a network This is the addressat which the data starts. verb to put thelocation data onto an address bus to iden-tify which word in memory or storagedevice is to be accessed A larger addressword increases the amount of memory acomputer can address.addressable adjective COMPUT able tobe addressed With the new operating sys-tem, all of the 5MB of installed RAM isaddressable.

addressable cursor noun COMPUT acursor which can be programmed to beplaced in a specific position

addressable point noun COMPUT in agraphics system, any point or pixel that canbe directly addressed

address base noun COMPUT a part of anaddress that defines the origin to which thelogical address is added

address book noun COMPUT 1. a list ofnode addresses 2. a list of the networkaddresses of other users to which elec-tronic mail can be sent

address bus noun COMPUT a physicalconnection that carries the address data inparallel form from the central processingunit to external devices

address code noun COMPUT a specialcode that identifies the part of a documentthat is an address

address format noun COMPUT a set ofrules defining the way the operands, dataand addresses are arranged in an instruc-tionaddressing noun COMPUT the process ofaccessing a location in memory

addressing mode noun COMPUT theway in which a location is addressed, e.g.sequential, indexed or direct

15 adiabatic heating address mapping noun COMPUT a vir-

tual address translated to an absoluteaddress

address mask noun COMPUT a patternof binary data bits that is used to block outparts of an address data word. It is usuallyused to separate the network and subnetparts of an address within a long Internet orIP address. The address mask 111000will block off the last three bits of anyaddress data.

address modification noun COMPUTthe changing of the address field, so that itcan refer to a different location

address register noun COMPUT a regis-ter in a computer that is able to store all thebits that make up an address which canthen be processed as a single unit (NOTE: Insmall micros, the address register is usu-ally made up of two data bytes.)

address resolution noun COMPUT theconversion of an Internet address into thecorrect physical network address that cor-responds to the distant computer orresource

address resolution protocol nounCOMPUT a protocol used within the TCP/IPstandard that is used to determine whetherthe source and destination address in apacket are in the data-link control (DLC)or Internet protocol (IP) format. Once theformat of the address is known, the packetcan be correctly routed over a network.Abbr ARP

address space noun COMPUT the totalnumber of possible locations that can bedirectly addressed by the program or CPU

address track noun COMPUT a track ona magnetic disk containing the addressesof files, etc., stored on other tracks

address word noun COMPUT a compu-ter word, usually made up, in a smallmicro, of two data words that contain theaddress data

add time noun MATHS a period of timetaken to perform one addition operationeither of a central processing unit or adderadduct verb PHYSIOL to pull towards thecentre line of the body noun CHEM achemical compound formed in an additionreaction between at least two differentcompounds or elementsadductor noun ANAT a muscle that pullsa leg or arm towards the central line of thebody or a toe or finger towards the axis ofa leg or arm

adenine noun BIOCHEM one of the fourbasic components of DNAadenosine noun BIOCHEM a compound,consisting of the base adenine and thesugar ribose, found in DNA, RNA andenergy-carrying molecules such as ATP

adenosine diphosphate noun BIO-CHEM full form of ADP

adenosine monophosphate nounBIOCHEM full form of AMP

adenosine triphosphate1 noun BIO-CHEM full form of ATP

adenosine triphosphate2 noun BIO-CHEM full form of ATPadenovirus noun MICROBIOL a virus thatcauses infections of the nose and throat inhumansadequate adjective sufficient The com-pressor must provide an adequate airflowthrough the engine. The brain must havean adequate supply of blood. Does thechildrens diet provide them with an ade-quate quantity of iron?ADH abbreviation BIOCHEM antidiuretichormoneadhere verb to attach firmly Clear iceadheres strongly to airframes.adhesion noun PHYS an intermolecularattraction between dissimilar materials thatare touching each other, causing them tostick togetheradhesive noun a glue A superglue isan all-purpose adhesive. adjective hav-ing the sticking quality of glue adhesivetape Adhesive bonding of aluminiumparts is widely employed.ADI abbreviation BIOL acceptable dailyintakeadiabatic adjective PHYS referring to achange in temperature in a mass of air as aresult of compression or expansion causedby an increase or decrease in atmosphericpressure without loss or gain of heat to orfrom its surroundings

COMMENT: A parcel of rising air expands,because the surrounding pressure falls.Also its temperature falls because no heatcan enter or leave it. If a parcel of airdescends, the opposite happens and the airtemperature rises.

adiabatically adverb PHYS without los-ing or gaining heat The air mass risesadiabatically through the atmosphere.

adiabatic heating noun PHYS the heat-ing of descending air caused by an increase

adiabatic lapse rate 16in atmospheric pressure without heat trans-fer, as when a bicycle pump is used

adiabatic lapse rate noun METEOROLthe rate at which air temperature decreasesas it rises above the Earths surface. lapserate

adipic acid noun CHEM a crystallinewhite solid used in nylon manufacture.Formula: C6H10O4.adipo- prefix BIOCHEM fatadipose adjective BIOCHEM containing ormade of fat

adipose tissue noun ANAT a type of tis-sue where the fibrous parts of cells arereplaced by fat when too much food iseatenaditus noun ANAT an opening or entranceto a passageadjacent adjective next to or near to They work in adjacent laboratories.

adjacent angle noun MATHS either ofthe two angles that are formed by the inter-section of two straight lines and lie on thesame side of one line

adjunct register noun COMPUT a 32-bitregister in which the top 16 bits are usedfor control information and only the bot-tom 16 bits are available for use by a pro-gramadjust verb to change something to bemore suitable or so that it works better We will have to adjust the next trial to takeaccount of recent results. This controladjusts the brightness and contrast of thescreen.

adjustable adjective designed to beadjusted An adjustable stop on the throt-tle control ensures a positive idling speed.adjustment noun 1. a change to improvethe setting or position of something Max-imum system pressure is often controlledby adjustment of the main engine-drivenpump. The brightness needs adjustment. The joystick needs adjustment as it some-times gets stuck. 2. BIOL a process of phys-ical change in response to externalenvironmental changesadjuvant noun 1. something added toimprove the effectiveness of somethingelse, e.g. a substance added to a pesticideto make it stick to waxy leaves 2. PHARM anagent added to a drug to improve its effec-tivenessadministrator noun COMPUT 1. a personwho manages an organisation, institutionor business 2. a person who is responsible

for looking after a network includinginstalling, configuring and maintaining itadmit verb to allow someone or some-thing to enter Cold air can be admittedthrough adjustable louvres or shutters.admittance noun PHYS a measure ofhow easily an electrical current can flowthrough a medium (NOTE: It is the recipro-cal of impedance.)adnexa plural noun ANAT structuresattached to an organadobe noun EARTH SCI 1. a fine clay fromwhich bricks can be made 2. bricks madefrom fine clay, dried in the sunadopt verb to choose to use or have some-thing as standard equipment or as a proce-dure We need to adopt a new strategy. The organisation has adopted strictenergy-saving measures.adoption noun the act or an instance ofusing something as standard equipment oras a procedure In spite of the adoption ofthe axial flow type compressor, someengines retain the centrifugal type.ADP noun 1. COMPUT data processingdone by a computer. Full form automaticdata processing 2. BIOCHEM a compoundinvolved in chemical reactions that releaselarge amounts of energy in the tissues ofliving organisms. Full form adenosinediphosphateADPCM abbreviation COMPUT adaptivedifferential pulse code modulationadrenal adjective ANAT situated near akidney

adrenal gland noun ANAT one of twoendocrine glands at the top of the kidneyswhich produce adrenaline and other hor-mones

adrenaline noun BIOCHEM a hormonesecreted by the medulla of the adrenalglands which has an effect similar to stim-ulation of the sympathetic nervous system(NOTE: The US term is epinephrine.)

COMMENT: Adrenaline is produced when aperson experiences surprise, shock, fear orexcitement. It speeds up the heartbeat andraises blood pressure. It is administered asan emergency treatment for acute anaphy-laxis and in cardiopulmonary resuscitation.

adrenergic adjective BIOL referring toneurons or receptors stimulated by adrena-line

COMMENT: Three types of adrenergicreceptor act in different ways when stimu-lated by adrenaline. Alpha receptorsconstrict the bronchi, beta 1 receptors

17 adventitiousspeed up the heartbeat and beta 2 recep-tors dilate the bronchi.

adrenoceptor noun ANAT a cell or neu-ron which is stimulated by adrenaline

adrenocorticotrophic hormonenoun BIOCHEM full form of ACTHadrenoreceptor noun ANAT same asadrenoceptorADSL noun COMPUT a high-speed trans-mission standard that uses the same wiresas a normal telephone service, but is muchfaster and provides a user with analways-on connection to the Internet sothere is no need to dial an access numberand no delay. Full form asymmetric dig-ital subscriber line (NOTE: Data is usuallytransferred from the Internet to the userscomputer at 2Mbps but transferred fromthe users computer to the Internet at aslower rate of 256Kbps.)adsorb verb CHEM (of a solid) to bondwith a gas or vapour which touches its sur-faceadsorbable adjective CHEM referring toa gas or vapour which is able to bond witha solid when it touches its surfaceadsorbate noun CHEM a substance that isadsorbedadsorbent CHEM adjective able to adsorbsomething such as a gas or vapour nouna solid which is able to bond with a gas orvapour which touches its surfaceadsorber noun a device which removesvolatile organic compounds from gas byadsorbing them to a carbon filteradsorption noun CHEM the bonding of asolid with a gas or vapour which touchesits surfaceadult BIOL adjective having reached matu-rity takes two years to reach the adultstage noun an organism that has reachedmaturityadvance noun 1. an instance of newdevelopment and progress advances ingene therapy 2. in advance of before verb to move or be moved forwards toadvance the ignition to adjust the timingof the ignition in an engine so that thespark occurs earlieradvanced adjective 1. modern andsophisticated advanced techniques 2.more complicated or more difficult to learn advanced mathematics 3. having devel-oped further the advanced stages of adisease 4. moved forwards the throttle

lever is advanced the throttle lever isphysically moved forwards

advanced gas-cooled reactor nounINDUST a type of nuclear reactor, in whichcarbon dioxide is used as the coolant and ispassed into water tanks to create the steamwhich will drive the turbines. Abbr AGR

advanced program to programcommunication noun COMPUT a set ofprotocols developed by IBM that allowspeer-to-peer communication betweenworkstations connected to an SNA net-work. Abbr APPC

Advanced Research ProjectsAgency Network noun COMPUT anoriginal network of interconnected com-puters, linked by leased lines, that formedthe first prototype for the current Internetand was developed by the US Departmentof Defense (Defense Advanced ResearchProjects Agency). Abbr ARPANET

advanced run-length limited nounCOMPUT a method of storing data onto ahard disk that is faster and more efficientthan RLL. Abbr ARLL

advanced technology attachmentpacket interface noun COMPUT a stand-ard interface that is used for CD-ROMs.Abbr ATAPIadvantage noun a good or beneficialfactor The multi-wheel combination hasthe advantage of smaller and lighterundercarriage structures. to take advan-tage of to get the most benefit from a situ-ation. Opposite disadvantageadvantageous adjective providing anadvantageadvect verb METEOROL (of air) to move ina horizontal direction due to convection Dispersal of hill fog takes place when sur-face heating lifts the cloud base or drier airis advected.advection noun METEOROL a movementof air in a horizontal direction. Compareconvection

advection fog noun a fog which formswhen warmer moist air moves over acolder surface, either land or seaadvent noun the arrival of something new With the advent of satellite navigationsystems, pilots of light aircraft have a moreaccurate means of knowing their position.adventitious adjective 1. BIOL on theoutside or in an unusual place 2. BOT refer-ring to a root which develops from a nodeon a plant stem and not from another root

adverse 18adverse adjective 1. bad or poor Adverse weather conditions delayed plant-ing. 2. harmful or unfavourable Thetreatment had an adverse effect on his der-matitis. She had an adverse reaction topenicillin. 3. moving in the opposite direc-tion adverse winds

adverse health effect noun a harmfuleffect on a persons health as a result ofcoming into contact with pollutants orallergens

adverse yaw noun AEROSP a sidewaysturn caused by aileron drag, in the oppositedirection to the direction of the intendedturnadvice noun a suggestion about whatshould be done The doctors advice wasto stay in bed. He took my advice andwent home. (NOTE: no plural: some adviceor a piece of advice)advisability noun the degree to which aparticular action is a good idea or notadvisable adjective to be recommended Where possible, it is advisable to closelycheck the condition of the tyres.advise verb 1. to inform someone 2. torecommend something to advise againstsomething to recommend that somethingshould not be doneadvisory adjective giving advice andinformation

advisory board, advisory committeenoun a group of specialists who can giveadvice

Advisory Committee on Releasesto the Environment noun an independ-ent advisory committee giving statutoryadvice to UK Government Ministers on therisks to human health and the environmentfrom the release and marketing of geneti-cally modified organisms (GMOs). It alsoadvises on the release of some non-GMspecies of plants and animals that are notnative to Great Britain. Abbr ACRE

advisory lock noun COMPUT a lockplaced on a region of a file by one processto prevent any other process accessing thesame data

advisory system noun COMPUT anexpert system that provides advice to a userAE abbreviation assimilation efficiencyAEA noun PHYS UKAEAAEBC abbreviation Agriculture, Environ-ment and Biotechnology Commission

AEC abbreviation PHYS Atomic EnergyCommission

aeolian deposits plural noun EARTHSCI sediments which are blown by thewind. loessaeon noun GEOL geological aeonaer- prefix CHEM airaerate verb 1. to put a gas, especially car-bon dioxide or air, into a liquid so that bub-bles are formed aerated water de-aerate 2. to allow air to enter a sub-stance, especially soil or water Wormsplay a useful role in aerating the soil.aeration noun CHEM 1. the process ofputting a gas, especially carbon dioxide orair, into a liquid The purpose of thebooster pump is to prevent fuel aeration. 2.the process of putting air into a substance aeration of the soil

COMMENT: The process of aeration of soil ismainly brought about by the movement ofwater into and out of the soil. Rainwaterdrives out the air and then, as the waterdrains away or is used by plants, fresh air isdrawn into the soil to fill the spaces. Theaeration process is also assisted bychanges in temperature, good drainage,cultivation and open soil structure. Sandysoils are usually well aerated. Clay soils arepoorly aerated.

aerator noun CHEM a device to put a gas,especially carbon dioxide or air, into a liq-uid. de-aeratoraerial adjective 1. referring to the air Some orchids have aerial roots. 2. AEROSPreferring to an aircraft in the air noun adevice to send or receive radio or TV sig-nals (NOTE: The US term for this meaningis antenna.)

aerial perspective noun COMPUT aview of a three-dimensional landscape as ifthe viewer is above the scene

aerial photography noun AEROSP pho-tography done from an aircraft in the air

aerial root noun BOT a root of someplants, which hangs above the ground orclings to other plants so that it can take upmoisture from the airaero- prefix AEROSP 1. air aerodynamic2. aircraft aero-engineaerobe noun MICROBIOL a living thing,particularly a microorganism, that needsoxygen for metabolism. Compare anaer-obeaerobic adjective BIOCHEM needing oxy-gen for its existence or for a biochemicalreaction to occur. Compare anaerobic

19 aestivation

aerobic decomposition noun BIO-CHEM the breakdown of organic materialby microorganisms without the presence ofoxygen

aerobic digester noun BIOCHEM adigester which operates in the presence ofoxygen

aerobic digestion noun BIOCHEM theprocessing of waste, especially organicwaste such as manure, in the presence ofoxygen

aerobic respiration noun BIOCHEM aprocess where the oxygen which isbreathed in is used to conserve energy asATPaerobiosis noun BIOCHEM a biologicalactivity which occurs in the presence ofoxygenaerodynamic adjective 1. referring tothe way in which objects are affected whenthey move through the atmosphere 2. refer-ring to a smooth rounded shape whichmoves easily through the air

aerodynamic braking noun AEROSPthe braking effect of drag

aerodynamic design noun ENG adesign of an aircraft or vehicle whichmoves easily through the air because of itsshape

aerodynamic forces plural noun PHYSforces of the air which act on aircraft inflightaerodynamics noun the science ofdynamics and interaction of movingobjects with the atmosphere (NOTE: takes asingular verb)aero-engine noun AEROSP an engineused in aircraft Most piston aero-enginesare cooled by air.aerofoil noun AEROSP a surface which isshaped to produce more lift than drag whenmoved through the air Wings, ailerons,elevators, fins and propellers are all exam-ples of aerofoils. (NOTE: The US term isairfoil.)aerogel noun CHEM a highly porous,extremely lightweight solid formed byreplacing the particles in a gel with a gasaerogenerator noun INDUST a windmillwith fast-moving sails used to generatemechanical power or electricityaerolisation, aerolization noun ENVI-RON the transmission of a substance in theform of a vapour or fine particles in the air

aeronautical adjective AEROSP referringto aeronautics

aeronautical engineering noun AER-OSP the science or study of the design ofaircraftaeronautics noun 1. AEROSP the scienceof aircraft design, construction, operationor navigation 2. NAVIG the theory and prac-tice of aircraft navigation (NOTE: takes asingular verb)aeroplane noun a power-driven, heav-ier-than-air craft with fixed wings (NOTE:Many people use the words aeroplaneand aircraft synonymously. However, aer-oplanes, hot-air balloons, helicopters, air-ships and gliders are all aircraft. The USterm is is airplane.)

aeroplane performance noun AER-OSP a description in figures regarding thespeed of the aircraft, rate of climb, lengthof take-off run, etc.aeroshell noun AEROSP the outer casingof a planetary landing spacecraft, designedto protect it from frictional heat generatedwhen it passes through an atmosphereaerosol noun 1. a quantity of tiny parti-cles of liquid suspended in a gas underpressure, sprayed from a container 2. a canof liquid with a propellant gas under pres-sure, which is used to spray the liquid inthe form of tiny drops 3. a quantity of tinyparticles of liquid or powder which staysuspended in the atmosphere

COMMENT: Aerosols in the atmosphere maybe formed of liquid, as in the case of mist, orof solid particles, as in the case of duststorms. Aerosols in the atmosphere are theform in which pollutants such as smoke aredispersed. Commercial aerosols use CFCsas propellants, but these are believed to beresponsible for the destruction of ozone inthe upper atmosphere and are graduallybeing replaced by less destructive propel-lants.

aerosol propellant noun a gas used inan aerosol can to make the spray of liquidcome outaerospace noun 1. METEOROL theEarths atmosphere and outer space 2. AER-OSP relating to the design, manufacture,and flight of vehicles or missiles that fly inand beyond the Earths atmosphere

aesthetic injury level noun the level atwhich the amenity benefits of pest controlbecome acceptable. Abbr AILaestivation noun 1. ZOOL dormancy insome animals such as lungfish during thesummer or periods of drought. Compare

aetiological agent 20hibernation 2. BOT the arrangement ofsepals and petals in a flower bud

aetiological agent noun BIOL an agentwhich causes a diseaseaetiology noun BIOL the causes of a dis-ease, or the study of those causesaffect verb to have an influence on or tochange something Humidity and air den-sity are factors which affect the output ofthe engine. Wind direction and speedonly affect the movement of the aircraftover the ground. Compare effectafferent adjective BIOL conducting liquidor electrical impulses towards the inside

afferent nerve noun ANAT same as sen-sory nerveaffinity noun CHEM an attraction betweentwo substances

affirmative acknowledgment nounTELECOM a signal from a receiver indicat-ing that it has accepted a message and isready for the next oneaffluent adjective 1. wealthy 2. EARTHSCI referring to water which is flowingfreely noun EARTH SCI a stream whichflows into a riverafforest verb AGRIC to plant an area withtreesafforestation noun 1. AGRIC the plantingof trees in an area or as a crop There islikely to be an increase in afforestation ofupland areas if the scheme is introduced. 2.EARTH SCI the planting of trees on land pre-viously used for other purposesaflatoxin noun FOOD INDUST a toxin pro-duced by species of the fungus Aspergillus,especially Aspergillus flavus, which growson seeds and nuts and affects stored grainAFLP abbreviation BIOTECH amplifiedfragment length polymorphismAFM abbreviation PHYS atomic forcemicroscopeAFP noun COMPUT a protocol used tocommunicate between workstations andservers in a network of Apple Macintoshcomputers. Full form Appletalk filing pro-tocolafrormosia noun TREES a hardwood treefrom West Africa, now becoming scarce.Latin name: Pericopisis elata.after- prefix coming laterafterburner noun a device whichreduces pollution by burning out organicgases

aftercare noun ENVIRON arrangementsfor preventing future pollution from anenvironmentally sensitive activity that hasceasedaftereffects plural noun BIOL changeswhich appear only some time after thecause The operation had some unpleas-ant aftereffects.afterglow COMPUT persistenceaftershock noun EARTH SCI a weakershock which follows the main shock of anearthquake. Compare foreshockAg symbol CHEM ELEM silveragamospermy noun BOT same asapomixisagar, agar agar noun BIOL a culturemedium based on an extract of seaweedused for growing microorganisms in labo-ratoriesagbiotech noun BIOTECH biotechnologyapplied to agriculture or an agriculturalindustryAGC noun ELECTRONICS an electronic cir-cuit that adjusts the level of an incomingsignal so that it is suitable for the next partof the circuit. Full form automatic gaincontrolage noun the number of years duringwhich a person or thing has existed Thesize varies according to age. verb to growold

age group noun all people of a particularageagency noun 1. an organisation or com-pany that acts as a representative for a per-son or business 2. a governmentorganisation with a specific role 3. BIOL theact of causing something to happen Thedisease develops through the agency ofbacteria present in the bloodstream.

Agenda 21 noun ENVIRON a global envi-ronmental programme and statement ofprinciples concerning sustainable develop-ment for the 21st century, agreed in 1992 atthe Earth Summit in Rio de Janeiro, Brazilagent noun 1. CHEM a chemical substancewhich causes a change an anti-icingagent 2. COMPUT a program or piece ofsoftware that runs on a workstation in anetwork, sending performance and statisti-cal information about the workstation to acentral network management console 3.COMPUT a series of commands or actionsthat are carried out automatically on a par-ticular file or data 4. BIOL a substance or

21 agriculturalorganism which causes a disease or condi-tion They identified the disease agent.

Agent Orange noun CHEM an extremelypoisonous herbicide used as a defoliant(NOTE: It was used by US forces in the Viet-nam War.)

age-related macular degenerationnoun MED an eye condition associated withageing in which the yellowish spot (mac-ula) in the middle of the retina breaksdown or becomes damaged as a result ofleaking blood vessels. Symptoms includeblurry central vision and diminished colourperception.

age-specific rate noun MED the numberof live births per 1000 women of a particu-lar age group per yearagglomerate noun EARTH SCI a rockmade up of fragments of lava fusedtogether by heatagglutinate verb BIOL to form intogroups or clustersagglutination noun BIOL a process inwhich cells come together to form clumps.For example, agglutination takes placewhen bacterial cells are in the presence ofserum or affects blood cells when blood ofdifferent types is mixed.

agglutination test noun 1. MICROBIOL atest used to identify bacteria 2. MED a testused to identify if a woman is pregnant

agglutination tests plural noun tests toidentify bacteriaagglutinin noun BIOCHEM a factor in aserum which makes cells group togetheragglutinogen noun BIOCHEM a factor inred blood cells which reacts with a specificagglutinin in serumaggravate verb to make somethingworse The effects of acid rain on the soilhave been aggravated by chemical runoff.aggregate noun 1. the total obtained byadding The aggregate of the capacity ofall the fuel tanks is 50 gallons. 2. COMPUTa collection of data objects 3. INDUSTcrushed stones used to make concrete orroad surfaces 4. EARTH SCI a mass of soiland rock particles stuck together verb tomake up a whole or total Ice crystalsaggregate to form snowflakes. to cometogether to form a mass

aggregate bandwidth noun the totalbandwidth of a channel carrying a multi-plexed data stream

aggregate function noun COMPUT amathematical database function performed

on a selected field in every record in aselected database

aggregate line speed noun COMPUTthe maximum speed at which data can betransmitted through a particular channel

aggregate operator noun COMPUT acommand in a database management pro-gram that starts an aggregate functionaggregation noun ECOL a dispersal pat-tern of plants or animals, where the indi-viduals remain quite close togetherAGN abbreviation ASTRON active galacticnucleusagnathan noun MARINE BIOL a sea verte-brate that has no jaw nor the two pairs offins or legs that are characteristic of verte-brates such as lampreys and hagfish. Sub-phylum: Agnatha. (NOTE: Modernexamples have eel-shaped bodies andslimy scaleless skin, but many extinctagnathans were covered with bony platesand scales.)agonist noun BIOCHEM a substance suchas a hormone, neurotransmitter or drug thatbinds to a cells receptors to trigger aresponseAGP abbreviation COMPUT acceleratedgraphics port (NOTE: This port does notreplace a PCI bus but works with it.)AGR abbreviation INDUST advancedgas-cooled reactoragree verb 1. to have the same idea oropinion about something 2. to come to anunderstandingagreed adjective generally accepted The millibar is an agreed unit of pressure.agreement noun the act or fact of havingthe same idea or opinion as somebodyagri- prefix AGRIC referring to agricultureor to the cultivation or management ofland. agro-agri-biotechnology noun biotechnol-ogy as applied to agricultureagribusiness noun AGRIC a large-scalefarming business run along the lines of aconventional company, often involving theprocessing, packaging and sale of farmproductsagricultural adjective AGRIC referring tofarmingAgricultural and Food ResearchCouncil noun formerly, a council estab-lished to organise and provide funds foragricultural and food research. It wasreplaced by the Biotechnology and Biolog-

agricultural engineer 22ical Sciences Research Council in 1993.Abbr AFRC

agricultural engineer noun AGRIC aperson trained in applying the principles ofscience to farming

agricultural engineering noun AGRICthe applying of the principles of science tofarmingagriculturalist noun AGRIC a persontrained in applying the principles of sci-ence to farming

agricultural waste noun AGRIC wast