The Collaborative International Dictionary of English v.0.48:

chalkboard \chalk"board`\ (ch[add]k"b[=o]rd`), n.
   a dark sheet of slate used as a surface for writing on, with
   chalk.

   Syn: blackboard.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

chalkboard
    n 1: sheet of slate; for writing with chalk [syn: blackboard,
         chalkboard]