Merriam-Webster Collegiate Dictionary - fail-safe

 I. adjective  Date: 1946  1. incorporating some feature for automatically counteracting the effect of an anticipated possible source of failure  2. being or relating to a safeguard that prevents continuing on a bombing mission according to a preconceived plan  3. having no chance of failure ; infallibly problem-free the little black dress…has consistently been the ~ solution for night — Vogue  II. noun  Date: 1975 a device or measure that makes something ~