| Acronym | Definition |
|---|
| A | Area |
| A | Activity |
| A | Approved |
| A | Accommodation |
| A | Atomic (as in A-bomb) |
| A | Ampere |
| A | Blood Type |
| A | Accusative |
| A | Battery Size |
| A | USDA Grade for Dairy Products and Eggs |
| A | About |
| A | To (Spanish, or from Latin ad) |
| A | Year |
| A | Are (unit of area) |
| A | Account |
| A | Advanced |
| A | Action |
| A | Article |
| A | Association |
| A | Author |
| A | Ask |
| A | Away (Sports) |
| A | Annual |
| A | Individual (IRB) |
| A | Analysis |
| A | Active |
| A | Administration |
| A | Agency |
| A | Answer |
| A | Apple |
| A | Excellent (scholastic grade) |
| A | Accept |
| A | Availability |
| A | Adult |
| A | Austria (international car index mark) |
| A | Academy |
| A | Assist (Sports) |
| A | Attack (US military aircraft designation, as in A-10) |
| A | Army (in combinations only) |
| A | Army |
| A | Australian |
| A | Alpha |
| A | Anonymous |
| A | Anna |
| A | Afternoon |
| A | Absolute (degrees Kelvin) |
| A | Ass |
| A | Amateur |
| A | Arc |
| A | Aircraft |
| A | Alto |
| A | Ace |
| A | Automobile |
| A | Ace (used on playing cards) |
| A | Analog |
| A | Agreed To (that an amendment or other matter was approved; US House) |
| A | Annually |
| A | Anterior |
| A | Acronym |
| A | Anchor (HTML) |
| A | Aqua |
| A | Adjacent (to a carboxyl group; chemistry) |
| A | Ante (Latin: Before) |
| A | Arctic |
| A | Anno |
| A | Aerial |
| A | Acre |
| A | Absent |
| A | Acceleration |
| a | Algemeen |
| A | Abbreviation |
| A | Airplane |
| A | Avance (French: fast) |
| A | Auditor |
| A | Applet |
| A | And |
| A | Artery |
| A | Airbus |
| A | Atto- |
| A | Allegro (game programming library) |
| A | Artillery |
| A | Amplitude |
| A | Asymmetric |
| A | Aft |
| A | Adjective |
| A | Arse |
| A | Adultery (as in the Scarlet Letter) |
| A | GMT + 1 hour |
| A | Argon |
| A | At or Above (constrained altitude) |
| A | Airman |
| A | Amphibian (aircraft type) |
| A | Newfoundland/Labrador (Canada Post designation) |
| A | Alanine |
| A | Anode |
| A | Adenosine |
| A | Autostrada (Italian notation for highways) |
| A | Accumulator |
| A | Adjutant |
| A | Adenine (one of four DNA building blocks) |
| A | Retinol (vitamin) |
| A | Auris (Latin: ear) |
| A | Angstrom (should be written with Å; unit of length) |
| A | Absorbance |
| A | Advanced Levels (highest level of academic boards, UK) |
| A | Analog Signal |
| A | Arterial blood |
| A | Animaniacs |
| A | Agouti |
| A | Atomic Mass |
| A | Analysis and Assessment (LANL) |
| A | Alpha Particle |
| A | Mass Number (physics) |
| A | Arterial Road (used with road numbers) |
| A | Total Acidity |
| A | Add(ed) (action code) |
| A | First in Series (chemistry) |
| A | Absorptance |
| A | American Bank Note Company (numismatic/philatelic) |
| A | Alwaya (dinnerware trademark) |
| A | Alveolar Gas |
| A | Advanced Digital Audio (filename extension) |
| A | Adenylic Acid |
| A | First Substrate |
| A | Assembly Source Code (Macintosh filename extension) |
| A | Avianca Airlines (philatelic airmail overprint) |
| A | Degree of Dissociation |
| A | Amendment of Application (insurance) |
| A | Aliphatic Chain (chemistry) |
| A | Nucleon Number (physics) |
| A | Helmholtz Energy |
| A | Specific Optical Rotation |
| A | Agilent Technologies Incorporated (stock symbol) |
| A | Smooth, Paintable (American Plywood Association Veneer Grades) |
| A | Specific Absorption Coefficient |
| A | Aromatic Substituent (chemistry) |
| A | Assisted Citizen (Alabama Public Safety Radio Code) |
| A | Aggressive Personality Type |
| A | Federal Reserve Bank of Boston, Massachusetts (designates original spot of circulation of a bill) |
| A | Applanation Tension (pressure in the eye) |
| A | Bunsen Solubility Coefficient |
| A | Stock and Bond Rating |
| A | Angle of Asymmetry (NIOSH) |
| A | Assay and Accountability (LANL) |
| A | Autotuned Navaid (aviation navigational aid) |
| A | Aktopia |
| A | Highest Level of Division I College Athletics (United States) |
| A | Accelerating Contactor or Relay |
| A | Lowest Full-Season Level (minor league baseball) |
| A | Undenominated US Stamp (15 cent, issued 22 May 78) |
| A | Air Force training category (15 days active duty training per year) |