The Collaborative International Dictionary of English v.0.48:

Swimmer \Swim"mer\, n.
   1. One who swims.
      [1913 Webster]

   2. (Far.) A protuberance on the leg of a horse.
      [1913 Webster]

   3. (Zool.) A swimming bird; one of the natatores.
      [1913 Webster]

   Little swimmer (Zool.), a phalarope.
      [1913 Webster]