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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 ?
Consequently, another drawer, and two porters, and several maids and the landlady, were all loitering by accident at various points of the road between the Concord and the coffee-room, when a gentleman of sixty, formally dressed in a brown suit of clothes, pretty well worn, but very well kept, with large square cuffs and large flaps to the pockets, passed along on his way to his breakfast.
What ship comes sailing home from India, and what English lady is this, married to a growling old Scotch Croesus with great flaps of ears?
It was in shape something like the cloak of a modern hussar, having similar flaps for covering the arms, and was called a Sclaveyn, or Sclavonian.
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.
Again he seized her, and at the same instant the flaps of the tent opened silently and a tall white man stood in the aperture.
The flaps of the cartridge boxes were all unfastened, and bobbed idiotically with each movement.
Their dark sunburned faces, and long flowing hair, their legging, flaps, moccasons, and richly-dyed blankets, and their painted horses gaudily caparisoned, gave them so much the air and appearance of Indians, that it was difficult to persuade one's self that they were white men, and had been brought up in civilized life.
I can quite understand that it's nicer to cover them with hair than with brass plates or leather flaps.
And, like Chanticleer at the sight of the sun, he flaps his wings and crows.
From the scraps we fashioned caps that came down around our ears, with flaps that fell about our shoulders and breasts.
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.
Under the canvas flaps along the thwarts, ready to hand for the rowers, were laid five of the Lee-Enfields.