The Collaborative International Dictionary of English v.0.48:
Flap \Flap\, n. [OE. flappe, flap, blow, bly-flap; cf. D. flap,
and E. flap, v.]
Anything broad and limber that hangs loose, or that is
attached by one side or end and is easily moved; as, the flap
of a garment.
A cartilaginous flap upon the opening of the larynx.
2. A hinged leaf, as of a table or shutter.
3. The motion of anything broad and loose, or a stroke or
sound made with it; as, the flap of a sail or of a wing.
4. pl. (Far.) A disease in the lips of horses.
5. (Aeronautics) a movable part of an airplane wing, used to
increase lift or drag, especially when taking off or
landing. used often in the plural.
Flap tile, a tile with a bent up portion, to turn a corner
or catch a drip.
Flap valve (Mech.), a valve which opens and shuts upon one
hinged side; a clack valve.