| Abbreviation | Definition |
|---|---|
| SIAM | Standards, Implementation, Action, Methodology |
| SIAP | Standards Implementation Action Plan |
| SIB | Special Intelligence Bureau |
| SIC | Standard Industrial Classification |
| SIC | Standard Industrial Code |
| SIC | Standard Industry Classification |
| SIC | Standard Industry Code |
| SID | Scientific Investigation Division |
| SIES | Office of Strategic Industries & Economic Security |
| SII | Science Information Infrastructure |
| SIM | Separatist Insurrectionary Movement |
| SIN | Signatures In Need |
| SIN | Special Item Number |
| SIP | Special Interest Program |
| SIP | Standards In Practice |
| SIPS | Side Intrusion Prevention System |
| SIR | Security Intelligence Report |
| SIS | Scientific Investigation Study |
| SITC | Standard International Trade Classification |
| SITES | Smithsonian Institution Traveling Exhibition Service |