keel

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A freight barge, especially one for carrying coal on the Tyne River in England.
• noun The load capacity of this barge.
• noun A British unit of weight formerly used for coal, equal to about 21.2 long tons.
• noun The principal structural member of a boat or ship, running along the center of the hull from bow to stern, to which the ribs are attached.
• noun A projecting ridge or fin on the bottom of the hull of a boat or ship that improves directional control and is often weighted for added stability.
• noun The principal structural member of an aircraft, resembling a ship's keel in shape and function.
• noun A structure, such as the breastbone of a bird, that resembles a ship's keel in function or shape.
• noun A pair of united petals in certain flowers, as those of many members of the pea family.
• intransitive & transitive verb To capsize or cause to capsize.
• transitive verb To make cool.

from The Century Dictionary.

• noun An early form of galley or small ship; a long boat: used with reference to Anglo-Saxon history.
• noun The principal timber in a ship or boat, extending from stem to stern at the bottom, supporting the whole frame, and consisting of a number of pieces scarfed and bolted together; in iron vessels, the combination of plates corresponding to the keel of a wooden vessel.
• noun In botany: A central longitudinal ridge along the back of any organ, as a leaf or glume.
• noun In a papilionaceous corolla, the lower pair of petals, which are more or less united into a prow-shaped body, usually inclosing the stamens and pistil.
• noun Another structure of similar form, as the lower petal in Polygala. Also called carina. See cut under banner.
• noun In zoology, a projecting ridge extending longitudinally along the middle of any surface.
• noun A ship.
• noun A strong, clumsy boat; a barge such as is used by the colliers at Newcastle in England.
• noun Hence A measure of coal, 8 Newcastle chaldrons, equal to 424 hundredweight.
• noun Red chalk; ruddle.
• To make cool; cool; moderate the heat of, as that of the contents of a pot boiling violently by gently stirring them.
• To moderate the ardor or intensity of; assuage; appease; pacify; diminish.
• To become cool; cool down.
• To mark, as a sheep, with ruddle.
• To plow with a keel, as the sea; navigate.
• To furnish with a keel.
• To turn up the keel; show the bottom.
• To give over; cease.
• To fall suddenly; tumble down or over, as from fright or a blow, or in a swoon.
• noun A variant of kail, 1.
• noun An obsolete or dialectal form of kill, kiln.
• noun In brewing, a broad flat vessel used for cooling liquids; a keelfat.
• noun In architecture, the projecting arris of an edge-molding.

from the GNU version of the Collaborative International Dictionary of English.

• noun (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. See Illust. of keelson.
• noun Fig.: The whole ship.
• noun engraving A barge or lighter, used on the Tyne for carrying coal from Newcastle; also, a barge load of coal, twenty-one tons, four cwt.
• noun (Bot.) The two lowest petals of the corolla of a papilionaceous flower, united and inclosing the stamens and pistil; a carina. See Carina.
• noun (Nat. Hist.) A projecting ridge along the middle of a flat or curved surface.
• noun (Aeronautics) In a dirigible, a construction similar in form and use to a ship's keel; in an aëroplane, a fin or fixed surface employed to increase stability and to hold the machine to its course.
• noun (Naut.) a keel peculiar to ironclad vessels, extending only a portion of the length of the vessel under the bilges.
• noun See under False.
• noun [U. S.] A low, flat-bottomed freight boat. See Keel, n., 3.
• noun one of the timbers or sections of which a keel is composed.
• noun in a level or horizontal position, so that the draught of water at the stern and the bow is the same.
• noun steady; balanced; steadily.
• noun A brewer's cooling vat; a keelfat.