Common words:
* Contrary: opposite in nature, direction, or meaning.
* Contrition: deep remorse for one's wrongdoing.
* Contradict: to speak against or deny the truth of something.
* Contrive: to plan or devise something, often in a clever or ingenious way.
* Control: to exercise power over or direct.
* Controversy: prolonged disagreement or debate.
* Counter: to act in opposition to.
* Counteract: to act against something to reduce its effect.
* Counterproductive: having the opposite of the desired effect.
Less common words:
* Contraband: goods that are illegally imported or exported.
* Contravene: to violate or break a law or rule.
* Contralto: the lowest female voice part.
* Contrarywise: on the other hand.
* Contretemps: an unexpected and unfortunate incident.
* Contratiempo: a rhythmic interruption or delay.
Note: The root "contr-" can sometimes be spelled "contra-".