[ feyl-seyf ]
See synonyms for fail-safe on
  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.

  1. (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.

  2. guaranteed to work; totally reliable: a fail-safe recipe for a cheese soufflé.

  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-saf·ing.
  1. to make fail-safe.

Origin of fail-safe

First recorded in 1945–50; apparently from verb phrase to fail safe(ly) Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2024

British Dictionary definitions for fail-safe


  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

  1. unlikely to fail; foolproof

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

Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012