English▸ adjective causing a piece of machinery or other mechanism to revert to a safe condition in the event of a breakdown or malfunction:
a forklift with a fail-safe device.
▪ unlikely or unable to fail:
the computer that runs the place is supposed to be fail-safe.
▸ noun [usually in singular] a system or plan that comes into operation in the event of something going wrong or that is there to prevent such an occurrence:
the secondary safety system is indeed a fail-safe.