fail-safe

American  

[feyl-seyf] / ˈfeɪlˌseɪf /

adjective

1. Electronics. pertaining to or noting a mechanism built into a system, as in an early warning system or a nuclear reactor, for insuring safety should the system fail to operate properly.

2. equipped with a secondary system that insures continued operation even if the primary system fails.

3. (sometimes initial capital letter) of, relating to, or designating a system of coded military controls in which bombers dispatched to a prearranged point as part of a standard operating procedure cannot advance farther without direct orders from a designated authority and cannot have the nuclear warheads they carry armed until they have passed their prearranged point.

4. guaranteed to work; totally reliable.

   a fail-safe recipe for a cheese soufflé.

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noun

1. (sometimes initial capital letter) the point beyond which the bombers cannot go without specific instruction; the fail-safe point.

2. something designed to work or function automatically to prevent breakdown of a mechanism, system, or the like.

verb (used with object)

fail-safed, fail-safing

1. to make fail-safe.

fail-safe British  

adjective

1. designed to return to a safe condition in the event of a failure or malfunction

2. (of a nuclear weapon) capable of being deactivated in the event of a failure or accident

3. unlikely to fail; foolproof

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verb

1. (intr) to return to a safe condition in the event of a failure or malfunction

Etymology

Origin of fail-safe

First recorded in 1945–50; apparently from verb phrase to fail safe(ly)

Example Sentences

The boats had rejected their inputs and automatically idled as a fail-safe, making them “dead” in the water.

From The Wall Street Journal • Nov. 27, 2025

Congress created the Insurrection Act as a fail-safe in response to armed mobs attacking their neighbors and organized militias seeking to overthrow elected officials.

From Los Angeles Times • Oct. 16, 2025

“Within moments, the robot came to a full stop in response to sensing a pedestrian in close proximity, which is considered its fail-safe state.”

From Los Angeles Times • Sep. 25, 2025

There was a fail-safe command that would temporarily render Ellie incapable of making decisions.

From Slate • Jan. 27, 2024

Upon arrival in the town or reservation, Irwin would trot the horses off the railcars and straight to the nearest back road or bullring, where he would implement a nearly fail-safe betting system.

From "Seabiscuit: An American Legend" by Laura Hillenbrand