from The American Heritage® Dictionary of the English Language, 4th Edition
- adj. Designed so as to be impervious to human incompetence, error, or misuse: a foolproof detonator; a foolproof safety lock.
- adj. Effective; infallible: a foolproof scheme.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- adj. For a device: protected, or designed to be proof against misuse or error; fail-safe.
- adj. For an idea or plan: infallible, or bulletproof.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- adj. not liable to failure
- v. proof against human misuse or error
fool + -proof (Wiktionary)