Source : Webster's Revised Unabridged Dictionary (1913)

Flapper \Flap"per\, n.
   1. One who, or that which, flaps.

   2. See {Flipper}. ``The flapper of a porpoise.'' --Buckley.

   {Flapper skate} (Zo["o]l.), a European skate ({Raia
      intermedia}).

Source : WordNet®

flapper
     n : a young woman in the 1920s who flaunted her unconventional
         conduct and dress