The Collaborative International Dictionary of English v.0.48:

Propeller \Pro*pel"ler\, n.
   [1913 Webster]
   1. One who, or that which, propels.
      [1913 Webster]

   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.
      [1913 Webster]

   3. A steamboat thus propelled; a screw steamer.
      [1913 Webster]

   Propeller wheel,the screw, usually having two or more
      blades, used in propelling a vessel.
      [1913 Webster]

WordNet (r) 3.0 (2006):

propeller
    n 1: a mechanical device that rotates to push against air or
         water [syn: propeller, propellor]