go ahead vs go-ahead

go ahead is not a noun while go-ahead is a noun.

Word	Noun	Adjective	Verb	Adverb
go ahead	No	No	Yes	No
go-ahead	Yes	No	No	No

go ahead (noun)	go-ahead (noun)
	readiness to embark on bold new ventures
	a signal to proceed

go ahead (verb)	go-ahead (verb)
proceed (with a plan of action)