flap
n. countablen. a flat piece of something that is attached on one side and can move up and down or back and forth. You often see these on pockets, boxes, or even on the wings of an airplane.
n. a flat, flexible piece of material attached at one edge, allowing it to hang loose or cover an opening. Often refers to mechanical surfaces on aircraft wings used to control lift.
He closed the flap of the envelope before mailing it.
The pilot adjusted the wing flaps to increase lift during the final approach to the runway.
A loose flap of canvas on the tent rattled incessantly against the poles as the wind picked up during the night.
From Middle English flap, flappe (“a slap; blow; buffet; fly-flap; something flexible or loose; flap”), related to Saterland Frisian Flappert (“wing, flipper”), Middle Dutch flabbe (“a blow; slap on the face; fly-flap; flap”) (modern Dutch flap (“flap”)), Middle Low German flabbe, vlabbe, flebbe, from the verb (see below). Related also to English flab and flabby.
From Middle English flappen (“to flap, clap, slap, strike”), related to Dutch flappen (“to flap”), German Low German flappen (“to flap”), German flappen (“to flap”), Dutch flabberen (“to flit, flap”). Probably ultimately imitative.
Commonly used to describe parts of clothing, packaging, or anatomical structures in medical contexts.