The Collaborative International Dictionary of English v.0.48:

dartboard \dartboard\, dart board \dart board\n.
   a circular board of wood or cork used as the target in the
   game of darts. It may have any of several patterns on it,
   such as concentric circles, or a central circle with rays.
   [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

dartboard
    n 1: a circular board of wood or cork used as the target in the
         game of darts [syn: dartboard, dart board]