The Collaborative International Dictionary of English v.0.48:
Keel \Keel\, n. [Cf. AS. ce['o]l ship; akin to D. & G. kiel
keel, OHG. chiol ship, Icel. kj[=o]ll, and perh. to Gr.
gay^los a round-built Ph[oe]nician merchant vessel, gaylo`s
bucket; cf. Skr. g[=o]la ball, round water vessel. But the
meaning of the English word seems to come from Icel. kj["o]lr
keel, akin to Sw. k["o]l, Dan. kj["o]l.]
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. See Illust. of Keelson.
2. Fig.: The whole 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.]
4. (Bot.) The two lowest petals of the corolla of a
papilionaceous flower, united and inclosing the stamens
and pistil; a carina. See Carina.
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 a["e]roplane, a fin
or fixed surface employed to increase stability and to
hold the machine to its course.
[Webster 1913 Suppl.]
Bilge keel (Naut.), a keel peculiar to ironclad vessels,
extending only a portion of the length of the vessel under
the bilges. --Ham. Nav. Encyc.
False keel. See under False.
(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.
Keel piece, one of the timbers or sections of which a keel
On even keel, in a level or horizontal position, so that
the draught of water at the stern and the bow is the same.
--Ham. Nav. Encyc.
On an even keel a. & adv., steady; balanced; steadily.