Pronunciation: ' f ā l- ˌ s ā f
Function: 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 >