Source : Webster's Revised Unabridged Dictionary (1913)

Planchet \Planch"et\, n. [F. planchette a small board, dim. of
   planche. See {Planch}.]
   A flat piece of metal; especially, a disk of metal ready to
   be stamped as a coin.

Source : WordNet®

planchet
     n : a flat metal disk ready for stamping as a coin [syn: {coin
         blank}]