| Abbreviation | Definition |
|---|---|
| CID | Central Intelligence Department |
| CID | Criminal Investigation Department |
| CIG | Central Intelligence Group |
| CINAL | Current INtelligence AnaLyses |
| CINRAD | Communist INfiltration of RADiation and Atomic Energy Program |
| CIP | Civilian Investigative Panel |
| CIP | Counter-Intelligence Program |
| CIPAV | Computer and Internet Protocol Address Verifier |
| CIRG | Critical Incident Response Group |
| CIRM | Communist Influence in Racial Matters |
| CJU | Criminal Justice Unit |
| CJX | Criminal Justice eXtranet |
| CK | Composite Killer |
| CL | Civil Litigation |
| CL | Closed |
| CMS | CoMmunist pro-Soviet |
| CMT | CoMmunist Trotskyism |
| CNDI | Confidential National Defense Informant |
| CO | Columbia Field Office |
| COC | Clash Of Clans |