The Collaborative International Dictionary of English v.0.48:

Propeller \Pro*pel"ler\, n.
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   1. One who, or that which, propels.
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   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.
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   3. A steamboat thus propelled; a screw steamer.
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   Propeller wheel,the screw, usually having two or more
      blades, used in propelling a vessel.
      [1913 Webster]