| Meaning | Category |
| Safety Institute of Australia | Community->Non-Profit Organizations |
| Samurai In Action | Miscellaneous->Science Fiction |
| Secretariat For Industrial Assistance | Governmental |
| Securities Industry Act | Business->General |
| Securities Industry Association | Business->General |
| Semiconductor Industry Association | Academic & Science->Electronics |
| Shadow Investigation Agency | Governmental->Police |
| Shuttle Induced Atmosphere | Governmental->NASA |
| Signal Apparel, Inc. | Business->NYSE Symbols |
| Society of Insurance Accountants | Business->Accounting |
| Software Impact Assessment | Governmental->NASA |
| Software Industry Association | Business->Professional Organizations |
| Solar Inertial Attitude | Governmental->NASA |
| Solidaridad Internacional Antifascista | International->Spanish |
| Special Instructional Assistance | Community->Educational |
| Spectrophotometric Intracutaneous Analysis | Medical->Physiology |
| Student Internet Association | Academic & Science->Universities |
| Students' Internet Association | Academic & Science->Universities |
| Superman's Insurance Agency | Miscellaneous->Funnies |
| Xi An, Mainland China | Regional->Airport Codes |
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