Sheet anchor and Safety valve

Sheet anchor noun - Spare anchor for use in emergency.

Safety valve and sheet anchor are semantically related. in security guarantee topic. In some cases you can use "Safety valve" instead a noun phrase "Sheet anchor".

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.

Sheet anchor and safety valve are semantically related. You can use "Sheet anchor" instead a noun phrase "Safety valve".