—adj. 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 cap.) of, pertaining 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.
—n. 1. (sometimes cap.) 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.