Source : Webster's Revised Unabridged Dictionary (1913)

Slot machine \Slot" ma*chine"\
   A machine the operation of which is started by dropping a
   coin into a slot, for delivering small articles of
   merchandise, showing one's weight, exhibiting pictures,
   throwing dice, etc.

Source : WordNet®

slot machine
     n : a machine that is operated by the insertion of a coin in a
         slot [syn: {coin machine}]