n.1. A timber that connects the keel and sternpost of a ship.
2. An arm extending to the rear of the keel to support the rudder and protect the propeller.
3. A fin projecting from the bottom of an outboard motor, used to protect the propeller and to provide extra steering control.
4. A centerboard mounted near the stern of a kayak, used to improve directional stability in windy weather.
5. A fin mounted near the tail of a surfboard, used to improve directional stability.