| Acronym | Meaning |
| A | Atomic (as in A-bomb) |
| A | Accelerating Contactor or Relay |
| A | Active |
| A | Add(ed) (action code) |
| A | Agreed To (that an amendment or other matter was approved; US House) |
| A | Air Force training category (15 days active duty training per year) |
| A | Airman |
| A | Airplane |
| A | Alpha |
| A | Analysis |
| A | Analysis and Assessment (LANL) |
| A | Army |
| A | Army (in combinations only) |
| A | Arterial Road (used with road numbers) |
| A | Artillery |
| A | Assay and Accountability (LANL) |
| A | Assisted Citizen (Alabama Public Safety Radio Code) |
| A | Attack (US military aircraft designation, as in A-10) |
| A | Automobile |
| A | Federal Reserve Bank of Boston, Massachusetts (designates original spot of circulation of a bill) |
| A | Individual (IRB) |
| A | Undenominated US Stamp (15 cent, issued 22 May 78) |