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.

---

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

---

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

As a key oil producer, Saudi Arabia is relied upon to surge output and stabilize markets during crises, but any physical degradation of its export capacity neuters this critical fail-safe.

From The Wall Street Journal • Mar. 2, 2026

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

There’s no 100% safe way to lift 500 pounds, just like there is no fail-safe way of throwing 100 mph.

From Los Angeles Times • Jul. 20, 2025

One significant solution implemented as a fail-safe for Level 4 automated vehicles is the concept of remote driving.

From Science Daily • Nov. 21, 2024

When the first seismic waves reached the power plant at Fukushima Daiichi, fail-safe systems shut down the reactors.

From "Meltdown" by Deirdre Langeland