foolproof

UK: /ˈfuːlpruːf/ US: /ˈfulˌpruf/ ,(fo̅o̅l′pro̅o̅f′)

WordReference Random House Learner's Dictionary of American English © 2026

fool•proof /ˈfulˌpruf/   adj. 

1. easy to use, operate, or understand;
   involving no risk:
   a foolproof VCR.
2. never-failing:
   a foolproof method.

WordReference Random House Unabridged Dictionary of American English © 2026

fool•proof  (fo̅o̅l′pro̅o̅f′), adj. 

1. involving no risk or harm, even when tampered with.
2. never-failing:
   a foolproof method.

• fool¹ + -proof 1900–05, American.

Collins Concise English Dictionary © HarperCollins Publishers::

foolproof / ˈfuːlˌpruːf/ adjective

1. proof against failure; infallible: a foolproof idea
2. (esp of machines) proof against human misuse, error, etc