Source : Webster's Revised Unabridged Dictionary (1913)

Flap \Flap\, v. t. [imp. & p. p. {Flapped}; p. pr. & vb. n.
   {Flapping}.] [Prob. of imitative origin; cf. D. flappen, E.
   flap, n., flop, flippant, fillip.]
   1. To beat with a flap; to strike.

            Yet let me flap this bug with gilded wings. --Pope.

   2. To move, as something broad and flaplike; as, to flap the
      wings; to let fall, as the brim of a hat.

   {To flap in the mouth}, to taunt. [Obs.] --W. Cartwright.

Source : WordNet®

flap
     n 1: any broad thin and limber covering attached at one edge;
          hangs loose or projects freely; "he wrote on the flap of
          the envelope"
     2: an excited state of agitation; "he was in a dither"; "there
        was a terrible flap about the theft" [syn: {dither}, {pother},
         {fuss}, {tizzy}]
     3: the motion made by flapping up and down [syn: {flapping}, {flutter},
         {fluttering}]
     4: a movable piece of tissue partly connected to the body
     5: a movable airfoil that is part of an aircraft wing; used to
        increase lift or drag [syn: {flaps}]
     [also: {flapping}, {flapped}]

flapping
     n : the motion made by flapping up and down [syn: {flap}, {flutter},
          {fluttering}]

flap
     v 1: move in a wavy pattern or with a rising and falling motion;
          "The curtains undulated"; "the waves rolled towards the
          beach" [syn: {roll}, {undulate}, {wave}]
     2: move noisily; "flags flapped in the strong wind"
     3: move with a thrashing motion; "The bird flapped its wings";
        "The eagle beat its wings and soared high into the sky"
        [syn: {beat}]
     4: move with a flapping motion; "The bird's wings were
        flapping" [syn: {beat}]
     5: make a fuss; be agitated [syn: {dither}, {pother}]
     6: pronounce with a flap, of alveolar sounds
     [also: {flapping}, {flapped}]

flapping
     See {flap}