| C | Carbon - Coulomb - One Hundred (in Roman Numerals) | - | Astronomy |
| C | Centi | - | Astronomy |
| C/O | Care Of (postal Code Indicating Temporary Address Change) | - | Astronomy |
| C/S/A | CINC | - | Astronomy |
| C2 OR C? | Command And Control | - | Astronomy |
| C2C | Consumer-To-Consumer Electronic Commerce - Cam-To-Cam Internet Chat | - | Astronomy |
| C2C | The British Rail Company Formerly Known As LTS Rail | - | Astronomy |
| C2D OR C?D | Intel Core 2 Duo - CERDEC Command And Control Directorate | - | Astronomy |
| C2IEDM OR C?IEDM | Command And Control Information Exchange Data Model | - | Astronomy |
| C2IS OR C?IS | Command And Control Information System | - | Astronomy |
| C2PC OR C?PC | Command And Control Personal Computer | - | Astronomy |
| C2V OR C?V | Command And Control Vehicle | - | Astronomy |
| C2W OR C?W | Command And Control Warfare | - | Astronomy |
| C3 OR C? | Colorectal Cancer Condition - Command | - | Astronomy |
| C3I OR C?I | Command | - | Astronomy |
| C4 OR C? | Command | - | Astronomy |
| C4I OR C?I | Command | - | Astronomy |
| C4ISR OR C?ISR | Command | - | Astronomy |
| CA | Calcium | - | Astronomy |
| CA | California (postal Symbol) - Canada (FIPS 10-4 Country Code; ISO 3166 Digram) - Catalonia -Civil Affairs - Close Armour - Computer Associates - Counter-Air | - | Astronomy |
| CA | Catalan Language (ISO 639-1 Code) | - | Astronomy |
| CAA | Canadian Automobile Association - (NORAD) Center For Aerospace Analysis - (U.S.) Center For Army Analysis - (U.S.) Clean Air Act - (U.S. Army) Concepts Analysis Agency - Civil Aviation Authority - Colonial Athletic Association | - | Astronomy |
| CAAT | OrCampaign Against Arms Trade - The Johns Hopkins Center For Alternatives To Animal Testing | - | Astronomy |
| CAC | California Association Of Criminalists - Chronic Asymptomatic [Disease] Carrier | - | Astronomy |
| CACM | Communications Of The ACM | - | Astronomy |
| CAD | Canadian Dollar (ISO 4217 Currency Code) -Computer-Aided Design - Computer-Aided Dispatch | - | Astronomy |
| CADCAM | Computer-Aided Design/Computer-Aided Manufacturing | - | Astronomy |
| CADMID | Concept | - | Astronomy |
| CADPAT | CAnadian Disruptive PATtern | - | Astronomy |
| CAE | Canadian Aviation Electronics (originally) - Certificate In Advanced English | - | Astronomy |
| CAEN | Close Action Engagement (constructive Simulation) | - | Astronomy |
| CAF | Central African Republic (ISO 3166 Trigram) -Confederation Of African Football (or French Conf?d?ration Africaine De Football) | - | Astronomy |
| CAFAD | Combined Arms For Air Defence | - | Astronomy |
| CAFDE | Canadian Association Of Film Distributors And Exporters - Computer Aided Federation Development Environment | - | Astronomy |
| CAFE | Corporate Average Fuel Economy Standard | - | Astronomy |
| CAI | Computer Assisted Instruction | - | Astronomy |
| CAIR | Council On American-Islamic Relations | - | Astronomy |
| CALABARZON | A Region In The Philippines: CAvite | - | Astronomy |
| CALL | (U.S.) Center For Army Lessons Learned | - | Astronomy |
| CAM | Chemical Agent Monitor - Computer-Aided Manufacturing | - | Astronomy |
| CAMRA | CAMpaign For Real Ale | - | Astronomy |
| CAN | Canada (ISO 3166 Trigram) | - | Astronomy |
| CANA | Convulsive Antidote | - | Astronomy |
| CANDU | CANada Deuterium Uranium (nuclear Reactor Design) | - | Astronomy |
| CANOLA | Canadian Oil | - | Astronomy |
| CAP | Combat Air Patrol - Civil Air Patrol - Common [Operating/Operational] Air Picture - Crisis Action Procedures - Common Agricultural Policy | - | Astronomy |
| CAPES | CAPability Evaluation System -Combined Arms Planning And Execution System | - | Astronomy |
| CARE | Community Database On Accidents On The Roads In Europe -Cooperative For Aid And Relief Everywhere (originally Cooperative For American Remittances To Europe) | - | Astronomy |
| CARMONETTE | Computerized Monte Carlo Simulation | - | Astronomy |
| CARP | Computed Air Release Point | - | Astronomy |
| CART | Championship Auto Racing Teams (now Defunct) | - | Astronomy |
| CAS | Chemical Abstracts Service - Chief Of The Air Staff - Close Air Support | - | Astronomy |
| CASE | Cellular Ammunition Storage Equipment - Computer-Aided Software Engineering | - | Astronomy |
| CASS | Command Activated Sonobuoy System | - | Astronomy |
| CASTFOREM | Combined Arms And Support Task FORce Evaluation Model | - | Astronomy |
| CASTOR | Canadian Automatic Small Telescopes For Orbital Research | - | Astronomy |
| CAT | Community Acceptance Testing - Computer-Assisted (or Axial) Tomography | - | Astronomy |
| CAT | Catalan Language (ISO 639-2 Code) | - | Astronomy |
| CATK | Counterattack | - | Astronomy |
| CATS | Computer Active Technology Suspension | - | Astronomy |
| CATT | Combined Arms Tactical Trainer | - | Astronomy |
| CAV | Cavalry | - | Astronomy |
| CAVOK | Ceiling And Visibility OK (Kav-okay) | - | Astronomy |
| CAW | Canadian Auto Workers Trade Union | - | Astronomy |
| CB | Cambodia (FIPS 10-4 Country Code) -Citizens' Band Radio | - | Astronomy |
| CBASSE | Commission On Behavioral And Social Sciences And Education (sea Bass) | - | Astronomy |
| CBC | Canadian Broadcasting Corporation - Christmas Bird Count - Cipher-Block Chaining - Cornering Brake Control | - | Astronomy |
| CBE | Commander Of The Order Of The British Empire - Cab Beside Engine (see Truck) | - | Astronomy |
| CBLA | Comparative Bullet Lead Analysis | - | Astronomy |
| CBM | Many | - | Astronomy |
| CBML | Coalition Battle Management Language | - | Astronomy |
| CBOL | Consortium For The Barcode Of Life | - | Astronomy |
| CBR | Case-Based Reasoning | - | Astronomy |
| CBRN | Chemical | - | Astronomy |
| CBRNE | Chemical, Biological, Radiological, Nuclear, Explosive | - | Astronomy |
| CBS | Columbia Broadcasting System - Corps Battle Simulation | - | Astronomy |
| CBT | Cognitive Behaviour Therapy -Combat | - | Astronomy |
| CC | Many | - | Astronomy |
| CCA | Counter Command Activity | - | Astronomy |
| CCC | Corpus Christi College | - | Astronomy |
| CCCP | Central Committee Of The Communist Party - Cyrillic For SSSR (Soyuz Sovetskikh Sotsialisticheskikh Respublik | - | Astronomy |
| CCD | Charge-Coupled Device | - | Astronomy |
| CCG | Canadian Coast Guard - Collectible Card Game | - | Astronomy |
| CCH | Computer-Controlled Hostile | - | Astronomy |
| CCIF | Comit? Consultatif International Des Communications T?l?phoniques ? Grande Distance (French For International Telephone Consultative Committee | - | Astronomy |
| CCII | Command And Control Information Infrastructure | - | Astronomy |
| CCIR | Comit? Consultatif International Pour La Radio (French For Consultative Committee On International Radio | - | Astronomy |
| CCIT | Comit? Consultatif International T?l?graphique (French For International Telegraph Consultative Committee | - | Astronomy |
| CCITT | Comit? Consultatif International T?l?phonique Et T?l?graphique (French For International Telegraph And Telephone Consultative Committee | - | Astronomy |
| CCK | Cholecystokinin -Cocos (Keeling) Islands (ISO 3166 Trigram) | - | Astronomy |
| CCOC | Canadian Children's Opera Chorus | - | Astronomy |
| CCOP | Coalition Common Operating/Operational Picture | - | Astronomy |
| CCP | Casualty Collection Point - Communications Checkpoint - Contingency Communications Package | - | Astronomy |
| CCRAP | Canadian Conservative Reform Alliance Party | - | Astronomy |
| CCRP | Command And Control Research Program | - | Astronomy |
| CCRTS | Command And Control Research And Technology Symposium | - | Astronomy |
| CCSCS | Consultative Committee For Space Data Systems | - | Astronomy |
| CCSIL | Command And Control Simulation Interface Language (cecil) | - | Astronomy |
| CCSK | Cyclic Code Shift Keying | - | Astronomy |
| CCT | Current Commitments Team | - | Astronomy |
