go-ahead vs traffic signal

go-ahead and traffic signal both are nouns.

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

As nouns, traffic signal is a hypernym of go-ahead; that is, traffic signal is a word with a broader meaning than go-ahead:

go-ahead: a signal to proceed
traffic signal: a visual signal to control the flow of traffic at intersections

Other hypernyms of go-ahead include stoplight, traffic light.

go-ahead (noun)	traffic signal (noun)
readiness to embark on bold new ventures	a visual signal to control the flow of traffic at intersections
a signal to proceed