All clear and Green light

All clear noun - A signal (usually a siren) that danger is over.

Green light and all clear are semantically related. in go-ahead topic. In some cases you can use "Green light" instead a noun phrase "All clear".

Green light noun - The approval by someone in authority for the doing of something.

All clear and green light are semantically related. You can use "All clear" instead a noun phrase "Green light".