Third-person singular simple present indicative form of faile

(obsolete) To come short of accomplishing (a purpose); to fail to do.

That cannot fail; sure to succeed.

(idiomatic) Certainly; by all means; as a matter of importance

Inevitably.

That does not cause undue damage in the event of failure. / Designed to shut off for safety if an emergency occurs.

A device, mechanism or measure designed to make something fail-safe.

To compensate automatically, in the event of a failure. / To make a device or mechanism fail-safe, or to add a fail-safe device or mechanism to an existing system.

(computing) To automatically switch processing from a failed component in a critical system to its live spare or backup component.

Of a device: such that, if it fails, it does so in a way that will cause little or no harm to other devices and personnel.