The Collaborative International Dictionary of English v.0.48:

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, gambling, etc.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

slot machine
    n 1: a machine that is operated by the insertion of a coin in a
         slot [syn: slot machine, coin machine]