Webster's English Dictionary

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rotor

ro.tor \'ro-t-*r\ n [contr. of rotator] 1: a part that revolves in a 
   stationary part; esp : the rotating me mber of an electrical machine 2: a 
   revolving vertical cylinder of a rotor ship  3: a complete system of more 
   or less horizontal blades that supplies all or  a major part of the force 
   supporting an aircraft in flight