The Dictionary of American Slang, Fourth Edition by Barbara Ann Kipfer, PhD. and Robert L. Chapman, Ph.D. Copyright (C) 2007 by HarperCollins Publishers. Cite This Source
Idioms and Phrases with one-armed bandit
A slot machine, as in It's amazing how many people think they can make money playing a one-armed bandit. This term refers to both appearance and function: the operating lever looks like an arm, and the machine in effect robs players, since it “wins” and keeps the player's money in an overwhelming majority of instances.
[ c. 1930