The Collaborative International Dictionary of English v.0.48:

Sundial \Sun"di`al\, n.
   An instrument to show the time of day by means of the shadow
   of a gnomon, or style, on a plate.
   [1913 Webster]

   Sundial shell (Zool.), any shell of the genus Solarium. See
      Solarium.
      [1913 Webster]

WordNet (r) 3.0 (2006):

sundial
    n 1: timepiece that indicates the daylight hours by the shadow
         that the gnomon casts on a calibrated dial