Noun | 1. | centreboard - a retractable fin keel used on sailboats to prevent drifting to leeward daggerboard - a removable centerboard on a small sailboat that can be lowered into the water to serve as a keel fin keel - a metal plate projecting from the keel of a shallow vessel to give it greater lateral stability sailboat, sailing boat - a small sailing vessel; usually with a single mast |