flap

Etymology 1

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.

noun

1. Anything broad and flexible that hangs loose, or that is attached by one side or end and is easily moved.
   a flap of a garment
   The envelope flap seemed curiously wrinkled.
   Again, Beside these parts destin'd to divers offices, there is a peculiar provision for the wind-pipe, that is, a cartilagineous flap upon the opening of the Larynx or Throttle, which hath an open cavity for the admiffion of the air 1686, Sir Thomas Browne, chapter VIII, in The Works of the Learned Sr. Thomas Brown: Containing, Enquiries Into Vulgar and Common Errors, etc, book IV
   The hairs guide the pollinating insect to the base of the petal, where there is a purplish nectary covered by a flap of tissue. 1998 October, Robert H. Mohlenbrock, “Twin Peaks”, in Natural History, volume 107, number 8, page 73
2. A hinged leaf.
   the flaps of a table
   the flap of a shutter
3. (aviation) A hinged surface on the trailing edge of the wings of an aeroplane, used to increase lift and drag.
4. A side fin of a ray.
5. The motion of anything broad and loose, or a sound or stroke made with it.
   the flap of a sail
   the flap of a wing
   Then he commenced to talk, really talk. and inside of two flaps of a herring's fin he had me mesmerized, like Eben Holt's boy at the town hall show. He talked about the ills of humanity, and the glories of health and Nature and service and land knows what all. 1913, Joseph C[rosby] Lincoln, chapter 4, in Mr. Pratt’s Patients, →OL
6. A controversy, scandal, stir, or upset.
   The comment caused quite a flap in the newspapers.
   “[…] We saw him vanish right in front of the rest of us. He was there and then he wasn’t. We were to wait for a year for his return or for some message. We waited. Nothing.” / Calvin, his voice cracking: “Jeepers, sir. You must have been in sort of a flap.” 1962, Madeleine L’Engle, “Absolute Zero”, in A Wrinkle in Time, New York, N.Y.: Ariel Books, →OCLC; republished New York, N.Y.: Ariel Books, 1973 printing, page 167
7. (phonetics) A consonant sound made by a single muscle contraction, such as the sound /ɾ/ in the standard American English pronunciation of body.
8. (surgery) A piece of tissue incompletely detached from the body, as an intermediate stage of plastic surgery.
9. (slang, vulgar, chiefly in the plural) The labia, the vulva.
10. (obsolete) A blow or slap (especially to the face).
    1450, Palladius on Husbondrieː Ware the horn and heels lest they fling a flap to thee.
    a1500 The Prose Merlinː The squire lift up his hand and gave him such a flap that all they in the chapel might it hear.
11. (obsolete) A young prostitute.
    Fall to your flap, my Masters, kisse and clip. […] Come hither, you foule flappes. 1631, James Mabbe, Celestina, IX. 110

Etymology 2

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.

verb

1. (transitive) To move (something broad and loose) up and down.
   The crow slowly flapped its wings.
   Startled, the wood pigeon flew off, its wings flapping noisily.
   He could be flapping his tongue about you right this minute to anybody who'll bloody listen. 2004, Robert Jordan, New Spring, page 316
2. (intransitive) To move loosely back and forth.
   The flag flapped in the breeze.
   Former Turkey goalkeeper Rustu Recber flapped at his first Delap throw but was given a soft free-kick by referee Antony Gautier. September 29, 2011, Tom Rostance, “Stoke 2 - 1 Besiktas”, in BBC Sport
3. (computing, telecommunications, intransitive) Of a resource or network destination: to be advertised as being available and then unavailable (or available by different routes) in rapid succession.