one-armed bandit

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A slot machine for gambling operated by pulling a lever on the side.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun gambling A gaming machine having a long handle (the “arm” referred to in the name) at one side that one pulls down to make reels spin; the player wins money or tokens when certain combinations of symbols line up on these reels.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a slot machine that is used for gambling