designating, of, or involving a procedure designed to prevent malfunctioning or unintentional operation, often specif. of nuclear-armed aircraft, through an intricate system of protective devices
See fail-safe in American Heritage Dictionary 4
(fālˈsāfˌ)
adjective
Capable of compensating automatically and safely for a failure, as of a mechanism or power source.
Acting to discontinue a military attack on the occurrence of any of various predetermined conditions.
Guaranteed not to fail: “There is no fail-safe mechanism guaranteed either to contain or to restore presidential authority”(Arthur M. Schlesinger, Jr.)