The Collaborative International Dictionary of English v.0.48:

Aileron \Ai"le*ron\ ([=a]"l[-e]*r[o^]n), n. [F., dim. of aile
   wing.]
   1. A half gable, as at the end of a penthouse or of the aisle
      of a church.
      [Webster 1913 Suppl.]

   2. (A["e]ronautics) A small plane or surface capable of being
      manipulated by the pilot of a flying machine to control
      lateral balance; a hinged wing tip; a lateral stabilizing
      or balancing plane.
      [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

aileron
    n 1: an airfoil that controls lateral motion