The Collaborative International Dictionary of English v.0.48:

handlebar \han"dle*bar`\ n.
   The curved bar connected by a shaft to the front wheel of a
   bicycle or motorcycle, positioned nearly horizontally in
   front of the rider's seat, designed to be gripped by the
   rider while riding, and used to steer the vehicle. Usually
   used in the plural; as, don't let go of the handlbars.
   [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

handlebar
    n 1: the shaped bar used to steer a bicycle