Source : Webster's Revised Unabridged Dictionary (1913)

Flap \Flap\, n. [OE. flappe, flap, blow, bly-flap; cf. D. flap,
   and E. flap, v.]
   Anything broad and limber that hangs loose, or that is
   attached by one side or end and is easily moved; as, the flap
   of a garment.

         A cartilaginous flap upon the opening of the larynx.
                                                  --Sir T.
                                                  Browne.

   2. A hinged leaf, as of a table or shutter.

   3. The motion of anything broad and loose, or a stroke or
      sound made with it; as, the flap of a sail or of a wing.

   4. pl. (Far.) A disease in the lips of horses.

   {Flap tile}, a tile with a bent up portion, to turn a corner
      or catch a drip.

   {Flap valve} (Mech.), a valve which opens and shuts upon one
      hinged side; a clack valve.