adj. 25B6; adjective INFALLIBLE, dependable, reliable, trustworthy, certain, sure, guaranteed, safe, sound, tried and tested; watertight, airtight, flawless, perfect; informal sure-fire; formal efficacious.
flawed.
FOOLPROOF
Meaning of FOOLPROOF in English
Concise Oxford thesaurus English vocabulary. Краткий оксфордский словарь английского языка тезаурус. 2012