Princeton's WordNet

1. foolproof, unfailing(verb)

   not liable to failure

   "a foolproof identification system"; "the unfailing sign of an amateur"; "an unfailing test"

2. goofproof, goof-proof, foolproof(verb)

   proof against human misuse or error

   "foolproof this appliance"

Kernerman English Learner's Dictionary

1. foolproof(adjective)ˈfulˌpruf

   certain to be successful

   a foolproof method of cooking rice

Wiktionary

1. foolproof(Adjective)

   For a device: protected, or designed to be proof against misuse or error; fail-safe.

2. foolproof(Adjective)

   For an idea or plan: infallible, or bulletproof.

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