The Collaborative International Dictionary of English v.0.48:

Flounder \Floun"der\, n. [Cf. Sw. flundra; akin to Dan. flynder,
   Icel. fly?ra, G. flunder, and perh. to E. flounder, v.i.]
   1. (Zool.) A flatfish of the family Pleuronectid[ae], of
      many species.
      [1913 Webster]

   Note: The common English flounder is Pleuronectes flesus.
         There are several common American species used as food;
         as the smooth flounder (P. glabra); the rough or
         winter flounder (P. Americanus); the summer flounder,
         or plaice (Paralichthys dentatus), Atlantic coast;
         and the starry flounder (Pleuronectes stellatus).
         [1913 Webster]

   2. (Bootmaking) A tool used in crimping boot fronts.
      [1913 Webster]