| Acronym | Meaning |
| CNWRA | Center For Nuclear Waste Regulatory Analyses |
| CO | Crystal Orbital |
| COA | Coenzyme A |
| COADS | Comprehensive Ocean-Atmosphere Data Set |
| COARE | Coupled Ocean-Atmosphere Response Experiment |
| COASTS | Coastal Ocean Advanced Science And Technology Study (IOC Program) |
| COBE | Cosmic Background Explorer Satellite (NASA) |
| COBRAS | Cosmic Background Radiation Anisotropy Satellite |
| COC | Cyclic Olefin Copolymers |
| COC | Cleveland Open Cup (Flash Point Test Method) |
| COC | Contaminants Of Concern |
| COC | Chain Of Custody |
| COCI | Committee On Chemistry And Industry (IUPAC) |
| COCP | Cut-off Coulomb Potential |
| COD | Chemical Oxygen Demand |
| COD | Continuous Optical Discharge |
| COD | Crack Opening Displacement |
| CODATA | Committee On Data For Science And Technology |
| CODEX | Centerband-only Detection Of Exchange |
| CODF | Crystallite Orientation Distribution Function |
| CODIS | Combined DNA Index System |
| COED | Computer Optimized Experimental Design |
| COF | Coefficient Of Friction |
| COG | Coke-oven Gas |
| COGS | Computer Oriented Geological Society |
| COH | Coefficient Of Haze |
| COHMAP | Cooperative Holocene Mapping Project |
| COHMED | Cooperative Hazardous Materials Enforcement Development Program |
| COHSEX | Coulomb-hole (plus) Screened-exchange (approxn. In Band-structure Calcns.) |
| COI | Constituents Of Interest |
| COIL | Chem. Oxygen-iodine Laser |
| COLD | Chronic Obstructive Lung Disease |
| COLD | Computer Output To Laser Disk |
| COLIWASA | Composite Liquid Waste Sampler |
| COLOC | Correlation Spectroscopy For Long-range Couplings |
| COLTRIMS | Cold-target Recoil-ion-momentum Spectroscopy |
| COMA | Cometary Mass Analyzer |
| COMA | Cyclic Olefin Maleic Anhydride |
| COMAH | Control Of Major Accident Hazards |
| COMARO | Composite Magic-angle Rotation |
| COMFA | Comparative Molecular Field Analysis |
| COMFET | Conductivity-modulated Field Effect Transistor |
| COMP | Cartilage Oligomeric Matrix Protein |
| COMPAS | Coating By Multiple Polyelectrolyte Adsorption Surface Activation |
| COMPREHEND | Community Programme Of Research On Environmental Hormones And Endocrine Disrupters |
| CONCAWE | Conservation Of Clean Air And Water In Western Europe [European Community Organization] |
| CONDO | Crystal Orbital Neglect Of Differential Overlap |
| CONFU | Conference On Fair Use |
| CONTOUR | Comet Nucleus Tour |
| CONTRAST | Connectivity Tracing Assignment Tools |