Airhole and Safety valve

Safety valve and airhole are semantically related. In some cases you can use "Safety valve" instead a noun "Airhole".

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.

Airhole and safety valve are semantically related. Sometimes you can replace term "Airhole" with "Safety valve", this terms are similar.