| | CIL | | Common Intermediate Language. |
| | CIL | | Critical Items List |
| | CIM | | come in mouth |
| | CIM | | Computer Interface module |
| | CIM | | Cum in mouth |
| | CIRT | | Computer Incident Response Teams |
| | CIS | | Compuserve Information Service |
| | CIS | | computer information science |
| | CIS | | customer Information Systems |
| | CISC | | Complex Instruction Set Computers |
| | CISG | | Contracts for the International Sale of Goods |
| | CISW | | Certified Independent Social Worker |
| | CITD | | center for international trade development |
| | CITD | | counter intelligence and terrorism division |
| | ciwwaf | | Cute Is What We Aim For |
| | CKIM | | Certified Knowledge and Innovation Manager |
| | CLDC | | Connected Limited Device Configuration |
| | CLI | | Caller Line Identification |
| | CLI | | Calling Line Identification |
| | CLI | | Command Line Interface |
| | clie | | communication, link, information and entertainment |
| | cm4agt | | call me for a good time |
| | CMA | | comparative market analysis |
| | CMAP | | Cover My Ass Partner |
| | CMAU | | cracking my ass up |
| | CMC | | Computer mediated communication |
| | CMF | | Count My Fingers |
| | CMH | | Cross My Heart |
| | CMIIAW | | Correct Me If I Am Wrong |
| | cmiiw | | correct me if I am wrong |
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