1.(Shipbuilding) A longitudinal timber, or series of timbers scarfed together, extending from stem to stern along the bottom of a vessel. It is the principal timber of the vessel, and, by means of the ribs attached on each side, supports the vessel's frame. In an iron vessel, a combination of plates supplies the place of the keel of a wooden ship.
3.A barge or lighter, used on the Tyne for carrying coal from Newcastle; also, a barge load of coal, twenty-one tons, four cwt. (Eng.)
5.(Nat. Hist.) A projecting ridge along the middle of a flat or curved surface.
6.(Aeronautics) In a dirigible, a construction similar in form and use to a ship's keel; in an aeroplane, a fin or fixed surface employed to increase stability and to hold the machine to its course.
Keel boat. (a)A covered freight boat, with a keel, but no sails, used on Western rivers. (U. S.)
(b)A low, flat-bottomed freight boat. See Keel, n., 3.