Definition of "Flap" :
noun: any broad thin and limber covering attached at one edge; hangs loose or projects freely
"He wrote on the flap of the envelope."
noun: a movable airfoil that is part of an aircraft wing; used to increase lift or drag
noun: a movable piece of tissue partly connected to the body
noun: the motion made by flapping up and down
noun: an excited state of agitation
"There was a terrible flap about the theft."
verb: pronounce with a flap, of alveolar sounds
verb: make a fuss; be agitated
verb: move noisily
"Flags flapped in the strong wind."
verb: move in a wavy pattern or with a rising and falling motion
verb: move with a flapping motion
"The bird's wings were flapping."
verb: move with a thrashing motion
"The bird flapped its wings."