flap

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A projecting or hanging piece usually attached to something on one side and often intended to protect or cover.
• noun Either of the folded ends of a book jacket that fit inside the front and back covers.
• noun A variable control surface on the trailing edge of an aircraft wing, used primarily to increase lift or drag.
• noun 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.
• noun The act of waving or fluttering.
• noun The sound produced by this motion.
• noun Linguistics A sound articulated by a single, quick touch of the tongue against the teeth or alveolar ridge, as (t) in water.
• noun Informal A commotion or disturbance.
• noun Archaic A blow given with something flat; a slap.
• intransitive verb To move (wings or arms, for example) up and down.
• intransitive verb To cause to move or sway with a fluttering or waving motion.
• intransitive verb To cause to strike against something.
• intransitive verb To move wings or the arms up and down.
• intransitive verb To fly by beating the air with the wings.
• intransitive verb To move or sway while fixed at one edge or corner; flutter.

from The Century Dictionary.

• noun In mycology, same as flab.
• noun In phonetics, a flapping motion of the tongue or uvula or the sound produced by it, as in vocalizing the letters l or r.
• To strike a blow with anything broad and flexible, as the hand; clap; make a noise like clapping.
• To move in a waving or swaying manner, as wings, or as something broad or loose.
• To burst out suddenly, as flames; flash.
• To fall like a flap, as the brim of a hat or other broad thing.
• To strike; beat; slap; give a stroke of any kind to.
• To beat with or as if with a flap.
• To make or cause a swaying movement of, as something broad or flap-like: as, the wind flapped the shutters.
• To provide with a flap.
• To let fall the flap of; move the flap of; especially, as in the case of a hat, to bring the flaps of forward and downward, so as to cover or protect the face.
• To arouse the attention of, as by flapping the ears: apparently in allusion to the “flappers” employed for such a purpose in the feigned island of Laputa in “Gulliver's Travels.” See extract from Swift, under flapper, 1.
• noun A stroke, blow, or buffet, as with the hand or with any weapon, etc.
• noun The motion of anything broad and loose; a flapping motion.
• noun An instrument for keeping off flies by a flapping motion.
• noun Anything broad and flexible that hangs loose, or is attached by one end or side, and easily moved; that part of anything which projects in such a form.
• noun A heavy valve used to prevent the entrance of the tide into a sewer.
• noun In surgery, a portion of skin or flesh separated from the underlying part, but remaining attached at the base.
• noun plural A disease in the lips of horses, in which they become blistered and swell on both sides.
• noun plural A discomycetous fungus, Peziza cochleata.
• noun plural A broadly expanded hymenomycetous fungus, probably Agaricus arvensis.

from the GNU version of the Collaborative International Dictionary of English.

• transitive verb To beat with a flap; to strike.
• transitive verb To move, as something broad and flaplike; ; to let fall, as the brim of a hat.
• transitive verb [Obs.] to taunt.
• intransitive verb To move as do wings, or as something broad or loose; to fly with wings beating the air.
• intransitive verb To fall and hang like a flap, as the brim of a hat, or other broad thing.
• noun Anything broad and limber that hangs loose, or that is attached by one side or end and is easily moved.
• noun A hinged leaf, as of a table or shutter.
• noun The motion of anything broad and loose, or a stroke or sound made with it.
• noun (Far.) A disease in the lips of horses.
• noun (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.
• noun a tile with a bent up portion, to turn a corner or catch a drip.