| Abbreviation | Definition |
|---|---|
| ARIMA | Auto Regressive Integrated Moving Average |
| ARISE | Arts Residency Interventions in Special Education |
| ARL | Army Research Laboratory |
| ARM | Atmospheric Radiation Measurement |
| ARMS | Acquisition Reform Model Sharing |
| ARNAV | American Reserve Naval Aviation Volunteers |
| ARNET | Acquisition Reform Network |
| ARO | Announcement of Research Opportunity |
| ARPA | Archaeological Resources Protection Act |
| ARRA | American Recovery and Reinvestment Act |
| ARRW | Air-Launched Repid Weapon |
| ARS | Agricultural Research Service |
| AS | American Samoa |
| AS | Applicability Statement |
| AS2 | Applicability Statement 2 |
| ASA | American Standards Authority |
| ASAC | As Soon As Convenient |
| ASAP | Automated Standard Application for Payments (used by the Commerce Department) |
| ASAVN | Aid to SouthEast Asia and Vietnam |
| ASC | Armed Services Committe |