Definition of "flap"

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

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

“[…] 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; republished New York, N.Y.: Ariel Books, 1973 printing, page 167

The current Middlesex grand jury […] is once again on the case, partly as the result of the public flap created by Brill's death and, of course, by the series of articles written by Corsetti in the month after Brill's demise.

1980 April 19, Mitzel, “Barbre Murder Grand Jury: Puccini Outtake”, in Gay Community News, page 1

Ware the horn and heels lest they fling a flap to thee.

1450, Palladius on Husbondrieː

The squire lift up his hand and gave him such a flap that all they in the chapel might it hear.

a1500 The Prose Merlinː

Fall to your flap, my Masters, kisse and clip. […] Come hither, you foule flappes.

1631, James Mabbe, Celestina, IX. 110

He could be flapping his tongue about you right this minute to anybody who'll bloody listen.

2004, Robert Jordan, New Spring, page 316

Former Turkey goalkeeper Rustu Recber flapped at his first Delap throw but was given a soft free-kick by referee Antony Gautier.

2011 September 29, Tom Rostance, “Stoke 2 - 1 Besiktas”, in BBC Sport‎