Source : Webster's Revised Unabridged Dictionary (1913)

Propeller \Pro*pel"ler\, n.
   1. One who, or that which, propels.

   2. A contrivance for propelling a steam vessel, usually
      consisting of a screw placed in the stern under water, and
      made to revolve by an engine; a propeller wheel.

Source : WordNet®

propeller
     n : a mechanical device that rotates to push against air or
         water [syn: {propellor}]