The Collaborative International Dictionary of English v.0.48:

dreidel \dreidel\, dreidl \dreidl\(dr[=a]d"'l), n.
   1. a toy shaped somewhat like a top, but having four flat
      sides, each marked with one of the Hebrew letters nun,
      gimel, he, or shin. It is spun like a top, and the letter
      showing when it stops spinning determines the outcome of a
      game of chance.
      [PJC]

   2. a game of chance played with a dreidel[1], most commonly
      by children at Hannukah.
      [PJC]