1. an extreme radical, especially in politics.
2. (in the French Revolution) a member of a radical society or club of revolutionaries that promoted the Reign of Terror and other extreme measures, active chiefly from 1789 to 1794: so called from the Dominican convent in Paris, where they originally met.
3. a Dominican friar.
4. (lowercase) one of a fancy breed of domestic pigeons having neck feathers that hang over the head like a hood.