clapperboard

from WordNet (r) 3.0 (2006)

clapperboard
    n 1: photographic equipment used to synchronize sound and motion
         picture; boards held in front of a movie camera are banged
         together

from The Collaborative International Dictionary of English v.0.48

clapperboard \clap"per*board`\ (kl[a^]p"p[~e]r*b[=o]rd`), n.
   a device which synchronizes sound and picture while making a
   motion picture, consisting of boards held in front of a movie
   camera, which are are banged together.
   [WordNet 1.5]