Fail-safe and Safety valve

Fail-safe noun - A measure taken to preclude loss or injury.

Safety valve and fail-safe are semantically related. In some cases you can use "Safety valve" instead a noun phrase "Fail-safe".

Safety valve noun - A valve in a container in which pressure can build up (as a steam boiler); it opens automatically when the pressure reaches a dangerous level.

Fail-safe and safety valve are semantically related. Sometimes you can use "Fail-safe" instead a noun phrase "Safety valve".