Nautical . a central fore-and-aft structural member in the bottom of a hull, extending from the stem to the sternpost and having the floors or frames attached to it, usually at right angles

sometimes projecting from the bottom of the hull to provide stability.

Literary . a ship or boat.

a part corresponding to a ship's keel in some other structure, as in a dirigible balloon.

( initial capital letter ) Astronomy . the constellation Carina.

Botany, Zoology . a longitudinal ridge, as on a leaf or bone; a carina.

Also called brace molding. Architecture . a projecting molding the profile of which consists of two ogees symmetrically disposed about an arris or fillet.

to turn or upset so as to bring the wrong side or part uppermost. ?

keel over,

to capsize or overturn.

to fall as in a faint

Several cadets keeled over from the heat during the parade.

on an even keel

in a state of balance; steady; steadily

The affairs of state are seldom on an even keel for long.

verb

black out , capsize , collapse , drop , faint , founder , go down , overturn , pass out , pitch , plunge , slump , swoon , topple , tumble , upset