foolproof
/ˈfuːlpruːf
/adjective
Incapable of going wrong or being misused: a foolproof security system...
- Bee-eaters have worked out a foolproof security system for the nest.
- True, democracy and the rule of law provide no foolproof security guarantee.
- Come up with a foolproof security system and stop other men like you from stealing priceless works of art.
Synonyms
infallible, never failing, unfailing, unerring, dependable, reliable, trustworthy, certain, sure, guaranteed, safe, sound, effective, efficacious, tried and tested;
watertight, airtight, flawless, perfect
informal sure-fire