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.

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

( sometimes initial capital letter ) 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.

guaranteed to work; totally reliable

a fail-safe recipe for a cheese soufflé.

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

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

to make fail-safe.

adjective

confident , covered , foolproof , protected , reliable , reliant , safeguarded , secure , sound , sure