| Abbreviation | Definition |
|---|---|
| CIA | Club for Improving Athletes |
| CIAA | Central Intercollegiate Athletic Association |
| CIASA | Cayman Islands Amateur Swimming Association |
| CIASA | Central Indiana Amateur Soccer Association |
| CIB | Christchurch Independent Bushballers |
| CIE | Cycling Is Easier |
| CIEE | Centro de Integra????o Empresa-Escola |
| CIG | Computer Interface Game |
| CILA | Canadian Intercollegiate Lumberjacking Association |
| CIN | Cincinnati Reds |
| CIRA | Canadian Intramural Recreation Association |
| CISAC | Canberra International Sports and Aquatic Centre |
| CISM | Counseil International de Sport Militaire |
| CIW | Champion In Waiting |
| CIWA | Canadian International Wrestling Association |
| CJ | Cricket Junior |
| CK | Charlie Knoll |
| CK | Coastal Kayak |
| CK | Crimson Knight |
| CKA | Canadian Killifish Association |