1 causing a piece of machinery to revert to a safe condition in the event of a breakdown or malfunction:
a forklift truck with a fail-safe device.
2 unlikely or unable to fail:
there is no guaranteed fail-safe procedure.
▸noun[usually in singular]a system or plan that comes into operation in the event of something going wrong or that is in place to prevent such an occurrence:
stewards positioned around the track as a fail-safe.
EnglishOxford Dictionary of English
