The Collaborative International Dictionary of English v.0.48:

Hurdy-gurdy \Hur"dy-gur`dy\, n. [Prob. of imitative origin.]
   1. A stringled instrument, lutelike in shape, in which the
      sound is produced by the friction of a wheel turned by a
      crank at the end, instead of by a bow, two of the strings
      being tuned as drones, while two or more, tuned in unison,
      are modulated by keys.
      [1913 Webster]

   2. In California, a water wheel with radial buckets, driven
      by the impact of a jet.
      [1913 Webster]

WordNet (r) 3.0 (2006):

hurdy-gurdy
    n 1: a musical instrument that makes music by rotation of a
         cylinder studded with pegs [syn: barrel organ, grind
         organ, hand organ, hurdy gurdy, hurdy-gurdy, street
         organ]