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a. A projecting or hanging piece usually attached to something on one side and often intended to protect or cover: the flap of an envelope.
b. Either of the folded ends of a book jacket that fit inside the front and back covers.
c. A variable control surface on the trailing edge of an aircraft wing, used primarily to increase lift or drag.
d. Medicine A piece of tissue that has been partially detached and used in surgical grafting to fill an adjacent defect or cover the cut end of a bone after amputation.
a. The act of waving or fluttering: the flap of the flag in the wind.
b. The sound produced by this motion.
3. Linguistics A sound articulated by a single, quick touch of the tongue against the teeth or alveolar ridge, as (t) in water. Also called tap1.
4. Informal A commotion or disturbance: a flap in Congress over the defense budget.
5. Archaic A blow given with something flat; a slap.
v. flapped, flap·ping, flaps
1. To move (wings or arms, for example) up and down.
2. To cause to move or sway with a fluttering or waving motion: The wind is flapping the tent fly.
3. To cause to strike against something: flapped the paper on the table.
a. To move wings or the arms up and down.
b. To fly by beating the air with the wings: The crow flapped away.
2. To move or sway while fixed at one edge or corner; flutter: banners flapping in the breeze.

[Middle English flappe, slap.]
ThesaurusAntonymsRelated WordsSynonymsLegend:
Noun1.flaps - a movable airfoil that is part of an aircraft wingflaps - a movable airfoil that is part of an aircraft wing; used to increase lift or drag
aerofoil, airfoil, control surface, surface - a device that provides reactive force when in motion relative to the surrounding air; can lift or control a plane in flight
landing flap - a flap on the underside of the wing that is lowered to slow the plane for landing
wing - one of the horizontal airfoils on either side of the fuselage of an airplane
References in classic literature ?
There stood by him, on each side, a young page with flaps in their hands, and when they saw he was at leisure, one of them gently struck his mouth, and the other his right ear; at which he startled like one awaked on the sudden, and looking towards me and the company I was in, recollected the occasion of our coming, whereof he had been informed before.
This flapper is likewise employed diligently to attend his master in his walks, and upon occasion to give him a soft flap on his eyes; because he is always so wrapped up in cogitation, that he is in manifest danger of falling down every precipice, and bouncing his head against every post; and in the streets, of justling others, or being justled himself into the kennel.
And then a reflection moved within the polished surface of the tiny glass, the man's eyes shot back out of space to the mirror's face, and in it he saw reflected the grim visage of Achmet Zek, framed in the flaps of the tent doorway behind him.
It was two hours later that the flaps at the front of the tent separated silently and gave entrance to a dark-robed figure, which passed noiselessly from the darkness without to the darkness within.
In the bottom of his heart each prayed that they might come safely through just this night, for they knew that during the morrow they would make the final stretch, yet the nerves of each were taut with strained anticipation of what gruesome thing might flap down upon them from the black sky, marking another for its own.
From hand to hand, the buckets went in the deepest silence, only broken by the occasional flap of a sail, and the steady hum of the unceasingly advancing keel.
But it was not so; in the evening poor Skye brought them back again, one by one in her mouth; not the happy little things that they were, but bleeding and crying pitifully; they had all had a piece of their tails cut off, and the soft flap of their pretty little ears was cut quite off.
Never did duster flap more briskly than the one Rose used that day, and never was a room "scrabbled" to rights in such haste as hers.
When she had slipped this on over her head, I exchanged the boy's cap she wore for a man's cap, large enough to cover her hair, and, when the flap was turned down, to completely cover her neck and ears.
Come and drink some beer with me at the Silenus," said the robust Ossipon after an interval of silence pervaded by the rapid flap, flap of the slippers on the feet of the Perfect Anarchist.
Distally based island fasciocutaneous flaps in the forearm offer simple and effective wound coverage.
Double flaps may be required to cover larger defects or where there is less expansibility of adjacent skin.