I. ˈfāl-ˌsāf 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 fail-safe solution for night — Vogue
II. noun
Date: 1975
: a device or measure that makes something fail-safe