A15 phases

Aardvark

Abaca

Abacus

ABC lipid transporter

Abdomen

Aberration (astronomy)

Aberration (optics)

Abrasive

Abscisic acid

Abscission

Absolute zero

Absorbable orthopedic implants

Absorption

Absorption (biology)

Absorption of electromagnetic radiation

Abstract algebra

Abstract data type

Acantharea

Acanthobdellida

Acanthocephala

Acanthodii

Acanthometrida

Acanthophractida

Acari

Accelerating universe

Acceleration

Acceleration analysis

Acceleration measurement

Accelerator mass spectrometry

Accelerometer

Acceptor atom

Access control models

Accident-tolerant fuels

Accoya wood

Acetal

Acetaminophen

Acetic acid

Acetone

Acetylcholine

Acetylene

Acheulean

Acid and base

Acid anhydride

Acid halide

Acid rain

Acid-base indicator

Acipenseriformes

Acoelomorpha

Aconchulinida

Acorales

Acoustic cloaking

Acoustic emission

Acoustic equivalent source methods

Acoustic impedance

Acoustic interferometer

Acoustic levitation

Acoustic microscope

Acoustic mine

Acoustic noise

Acoustic phonetics

Acoustic radiation pressure

Acoustic radiometer

Acoustic signal processing

Acoustic torpedo

Acoustic viscometer

Acoustical holography

Acoustical properties of nontraditional woods

Acoustics

Acoustooptic imaging

Acoustooptics

Acquired immune deficiency syndrome (AIDS)

Acquired immunological tolerance

Acrothoracica

Acrotretida

Acrylonitrile

Actiniaria

Actinide elements

Actinium

Actinobacillus

Actinomycetes

Actinophryida

Actinopodea

Actinopterygii

Action

Activated carbon

Activation analysis

Active materials and smart structures

Active noise control in vehicles

Active sound control

Active Thermochemical Tables

Active traffic management

Activity (thermodynamics)

Activity-based costing

Acylation

Adaptation (biology)

Adaptive control

Adaptive management

Adaptive middleware

Adaptive optics