| Consolidated Isotropically, sheared undrained | Academic & Science |
| Columbia International University | Academic & Science |
| California International University | Academic & Science |
| Commercial Insurance Underwriters | Business |
| Community Intelligence Unit | Community |
| Committee for an Inclusive University | Community |
| Confederation of Independent Unions | Community |
| Club and Institute Union | Community |
| Christ In Us | Community |
| Confederation of Independent Unions in the Public Sector | Community |
| Criminals In Uniform | Community |
| Confederazione Italiana Unionquadri | Community |
| Culture Identity Unitpacks | Community |
| Common Interchange Unit | Computing |
| Central Intermediate Unit | General |
| Conviction Integrity Unit | General |
| Control Interface Unit | General |
| Central Intelligence Unit | General |
| Critical Incident Unit | General |
| Customer Interface Unit | General |
| Categorical Industrial User | General |
| Custom Installer Ultimate | General |
| Center for International Understanding | General |
| Communication Interface Unit | General |
| Clone Intelligence Unit | General |
| champion in U | General |
| Communication Interface Unite | General |
| Criminal Interdiction Unit | Governmental |
| Criminal Information Unit | Governmental |
| Criminal Investigations Unit | Governmental |
| Customs Investigation Unit | Governmental |
| Criminal Investigation Unit | Governmental |
| Criminal Investigative Unit | Governmental |
| Customs and Immigration Union | Governmental |
| Collision Investigation Unit | Governmental |
| Convergència i Unió | International |
| Clean It Up | Internet |
| Clinical Investigations Unit | Medical |
| Clinical Investigation Unit | Medical |
| Cardiac Investigation Unit | Medical |
| Chronic Idiopathic Urticaria | Medical |
| Cell Interface Unit | Military and Defence |
| Chippewa County International Airport, Sault Ste Marie, Michigan USA | Regional |
| Computer Interface Unit | Space Science |
| Controller Interface Unit | Space Science |
| Communications Interface Unit | Telecommunication |