| conundrum | A confusing and difficult problem or question | |
| copious | Abundant in supply or quantity | |
| cordial | Warm and friendly | |
| corroborate | To confirm or support something with additional evidence; to make more certain | |
| cosmopolitan | Familiar with and at ease in many different countries and cultures | |
| covert | Not openly acknowledged or displayed | |
| cowed | To frighten with threats or a show of force | |
| crepuscular | of, resembling, or relating to twilight | |
| demotic | Relating to ordinary people and their language; popular or colloquial | |
| demur | Raise doubts or objections or show reluctance | |