a strong piece or beam of wood or metal center of the bottom of a ship or boat. The keel is the main support of a ship and the whole frame or hull is attached to it. Also, a fin or flat-shaped piece that is attached lengthwise to the bottom of a sailboat and hangs down into the water. The keel keeps the sailboat upright so it will not tip over and prevents it from being blown sideways by the wind. —Welcome to the SO Glossary Final approval 2-Mar-90