The Collaborative International Dictionary of English v.0.48:

autogiro \autogiro\ n.
   same as autogyro.

   Syn: autogyro, gryoplane
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

autogiro
    n 1: an aircraft that is supported in flight by unpowered
         rotating horizontal wings (or blades); forward propulsion
         is provided by a conventional propeller [syn: autogiro,
         autogyro, gyroplane]