| A | Acro (joke Acronym) | - | Astronomy |
| A | Ampere | - | Astronomy |
| A | Atto | - | Astronomy |
| A&S | Armament & Standardisation | - | Astronomy |
| A.K.A. | Also Known As | - | Astronomy |
| A/C | Air Conditioned/Conditioning - Aircraft | - | Astronomy |
| A/D | Analog/Digital | - | Astronomy |
| A/S | Anti-submarine | - | Astronomy |
| A2ATD OR A?ATD | Anti | - | Astronomy |
| A2C2 OR A?C? | Army Airspace Command And Control | - | Astronomy |
| A4 | Many | - | Astronomy |
| AA | Achieved Availability - Alcoholics Anonymous -Armed Forces Americas (postal Symbol) - Aruba (FIPS 10-4 Territory Code) -Assembly Area - Automobile Association- Avenue Of Approach | - | Astronomy |
| AA | Afar Language (ISO 639-1 Code) | - | Astronomy |
| AA | Attoampere | - | Astronomy |
| AAA | Administration | - | Astronomy |
| AAAI | American Association For Artificial Intelligence | - | Astronomy |
| AAAS | American Association For The Advancement Of Science | - | Astronomy |
| AAAV | Advanced Amphibious Assault Vehicle | - | Astronomy |
| AAC | Army Air Corps (British Army) | - | Astronomy |
| AAD | Analogue-Analogue-Digital (CD Quality) - Australian Antarctic Division | - | Astronomy |
| AADAC | Alberta Alcohol And Drug Abuse Commission | - | Astronomy |
| AADC | Area Air Defence Commander | - | Astronomy |
| AADD | Atlanta Alliance On Developmental Disabilities | - | Astronomy |
| AADT | Annual Average Daily Traffic Flow | - | Astronomy |
| AAFC | U.S. Army Air Corps Ferrying Command (1941-1942) - All-America Football Conference (1946?1949) | - | Astronomy |
| AAFES | Army And Air Force Exchange Service | - | Astronomy |
| AAI | Applied Artificial Intelligence | - | Astronomy |
| AAIS | Advanced Airborne Interceptor Simulator | - | Astronomy |
| AAM | Air-to-Air Missile | - | Astronomy |
| AAN | American Academy Of Nursing | - | Astronomy |
| AANEAS | Anglo-Australian Near-Earth Asteroid Survey | - | Astronomy |
| AAODL | Atmospheric Aerosols And Optics Data Library | - | Astronomy |
| AAP | Advanced Acquisition Plan - Allied Administrative Publication - American Academy Of Pediatrics | - | Astronomy |
| AAPC | Accounting And Auditing Policy Committee | - | Astronomy |
| AAR | After-Action Review - Association Of American Railroads | - | Astronomy |
| AAR | Afar Language (ISO 639-2 Code) | - | Astronomy |
| AARP | (i/s) American Association Of Retired Persons (now Officially Known Only By The Initials) | - | Astronomy |
| AAS | Advanced Automation System - American Astronomical Society (double-A-S) | - | Astronomy |
| AASPEM | Advanced Air-to-air System Performance Evaluation Model | - | Astronomy |
| AAT | Australian Antarctic Territory | - | Astronomy |
| AAV | Amphibious Assault Vehicle | - | Astronomy |
| AAWC | Anti-Air Warfare Commander | - | Astronomy |
| AB | Able Seaman (rank) | - | Astronomy |
| AB | Abkhaz Language (ISO 639-1 Code) | - | Astronomy |
| ABA | American Bar Association - American Basketball Association - American Beverage Association - American Bicycle Association - American Birding Association - Australian Broadcasting Authority | - | Astronomy |
| ABB | ASEA Brown Boveri (Swiss-Swedish Multinational Company) | - | Astronomy |
| ABBA | Agnetha | - | Astronomy |
| ABC | Abstinence | - | Astronomy |
| ABCA | American Border Collie Association - American | - | Astronomy |
| ABCS | (U.S.) Army Battle Command System | - | Astronomy |
| ABET | Accreditation Board For Engineering And Technology | - | Astronomy |
| ABIN | Ag?ncia Brasileira De Intelig?ncia (Brazilian Intelligence Agency) | - | Astronomy |
| ABK | Abkhaz Language (ISO 639-2 Code) | - | Astronomy |
| ABL | American Basketball League | - | Astronomy |
| ABLE | AirBorne Law Enforcement (police Air Support Unit) | - | Astronomy |
| ABM | Anti-Ballistic Missile - Asynchronous Balanced Mode - Automated Banking Machine | - | Astronomy |
| ABMC | American Battle Monuments Commission | - | Astronomy |
| ABN | Australian Business Number (a Number Issued By The Australian Government As Registration Of A Business And Used For Taxation Purposes) | - | Astronomy |
| ABPI | Association Of The British Pharmaceutical Industry | - | Astronomy |
| ABRSM | Associated Board Of The Royal Schools Of Music | - | Astronomy |
| ABS | Acrylonitrile Butadiene Styrene - Anti-lock Braking System | - | Astronomy |
| ABSA | Amalgamated Banks Of South Africa (ab-sa) | - | Astronomy |
| ABSTRIPS | Abstraction-Based STRIPS | - | Astronomy |
| ABW | Aruba (ISO 3166 Trigram) | - | Astronomy |
| AC | Adriamycin-Cyclophosphamide (chemotherapy) - Air Conditioning - Alternating Current - Ante Christum (Latin | - | Astronomy |
| AC | Actinium | - | Astronomy |
| AC | Attocoulomb | - | Astronomy |
| ACA | Airspace Control Authority - Airspace Co-ordination Area - A Current Affair | - | Astronomy |
| ACARS | Aircraft Communication Reporting System | - | Astronomy |
| ACAS | Aboriginal Children's Advancement Society - Advisory | - | Astronomy |
| ACB | Asociaci›n De Clubs De Baloncesto (Spanish For Association Of Basketball Clubs) | - | Astronomy |
| ACC | U.S. Air Combat Command - Air Component Commander - Altocumulus Castellanus - Atlantic Coast Conference - Automatic Climate Control - Area Control Center | - | Astronomy |
| ACCA | Automatic Cloud Cover Assessment | - | Astronomy |
| ACCAC | Awdurdod Cymwysterau | - | Astronomy |
| ACCD | American Coalition Of Citizens With Disabilities | - | Astronomy |
| ACCS | Air Communications And Control Squadron | - | Astronomy |
| ACDA | Arms Control & Disarmament Agency | - | Astronomy |
| ACDC | Alternating Current Direct Current | - | Astronomy |
| ACE | Air Combat Emulator (computer Game) - Allied Command Europe - Armored Combat Earthmover - Automatic Computing Engine | - | Astronomy |
| ACES | Aerolineas Centrales De Colombia | - | Astronomy |
| ACF | American Car And Foundry - American Culinary Federation - Administration For Children And Families | - | Astronomy |
| ACHT | Average Call Hold Time | - | Astronomy |
| ACID | Atomicity | - | Astronomy |
| ACINT | Acoustic Intelligence | - | Astronomy |
| ACK | Acknowledge (telecommunications; Cf. NAK) | - | Astronomy |
| ACL | Access Control List - Anterior Cruciate Ligament | - | Astronomy |
| ACLOS | Automatic CLOS (missile Control System) | - | Astronomy |
| ACLS | Alternate Crops And Systems Lab | - | Astronomy |
| ACLU | American Civil Liberties Union | - | Astronomy |
| ACM | Many | - | Astronomy |
| ACMC | (U.S.) Assistant Commandant Of The Marine Corps | - | Astronomy |
| ACN | Airborne Communications Node - Australian Company Number (number Issued By The Australian Government As Registration Of A Limited Liability Company) | - | Astronomy |
| ACO | Airspace Control Order | - | Astronomy |
| ACOBA | Advisory Committee On Business Appointments | - | Astronomy |
| ACOG | American College Of Obstetricians And Gynecologists | - | Astronomy |
| ACOM | (U.S.) Atlantic Command | - | Astronomy |
| ACORN | Association Of Community Organizations For Reform Now | - | Astronomy |
| ACP | Air Control Point | - | Astronomy |
| ACR | Advanced Concepts And Requirements | - | Astronomy |
| ACRI | African Crisis Initiative | - | Astronomy |
