| A&P | The Great Atlantic and Pacific Tea Company 
| Others |
| A&PS | Administration and Program Support (MSFC Directorate)
| Others |
| A&Q | Alert and Que
| Others |
| A&R | Advanced and Research
| Others |
| A&R | Alert and responsive
| Others |
| A&R | Analysis and Reporting
| Others |
| A&R | Artists and Repertoire
| Others |
| A&R | Assembly and Repair
| Others |
| A&R | Automation and Robotics
| Others |
| A&RC | Application and Resource Control
| Others |
| A&S | Accident & Sickness
| Others |
| A&S | Activities & Services
| Others |
| A&S | Administrative & Services
| Others |
| A&S | Anagrams & Scrambles
| Others |
| A&S | Arts and Sciences
| Others |
| A&T | Acquisition and Technology
| Others |
| A&T | Architecture and Transport
| Others |
| A&T | Automotive and Transportation
| Others |
| A&T | Ayo & Teo
| Others |
| A&T | North Carolina Agricultural & Technical State University
| Others |
| A&TA | Assembly and Test Area
| Others |
| A&V | Assembly and Verification
| Others |
| A&V | Audio and Video
| Others |
| A&W | Alive and Well
| Others |
| A&W | Amburgers and Wootbeer
| Others |
| A+I | Architecture + Interiors magazine
| Others |
| A-2 | Intelligence Staff section of United States Army Air Corps
| Others |
| A-3 | Air Force Operations Directorate
| Others |
| A-4 | Air Force Logistics Directorate
| Others |
| A-5 | Air Force Plans Directorate
| Others |
| A-A | Anti-Aircraft
| Others |
| A-BUG | AdSonar - Bulk Upload Gateway
| Others |
| A-CDM | Airport-Collaborative-Decision-Making
| Others |
| A-D | Analog to Digital
| Others |
| A-F | Acid-Free
| Others |
| A-GEMTF | Advanced Generic Equipment Model Task Force
| Others |
| A-GPS | Assisted Global Positioning System
| Others |
| A-GPS | Augmented Global Positioning System
| Others |
| A-M | Alternating Maximization
| Others |
| A-M | Artery-to-Muscle
| Others |
| A-MAC | Adaptive Media Access Control
| Others |
| A-OLS | Administrators Online
| Others |
| A-P | Anterior-Posterior
| Others |
| A-Si | Amorphous Silicon
| Others |
| A-T | Ataxia-telangiectasia
| Others |
| A-TEAM | Alpha from the title Operational Detachment Alphas
| Others |
| A-V | Arterio-Venous
| Others |
| A-V | ArterioVenous
| Others |
| A-VO2 | Arterio-Venous Oxygen
| Others |
| A-VO2 | ArterioVenous Oxygen
| Others |