go back vs regress

go back is not a noun while regress is a noun.

Word	Noun	Adjective	Verb	Adverb
go back	No	No	Yes	No
regress	Yes	No	Yes	No

As verbs, regress is a hypernym of go back; that is, regress is a word with a broader meaning than go back:

Other hypernyms of go back include retrovert, return, revert, turn back.

go back (noun)	regress (noun)
	returning to a former state
	the reasoning involved when you assume the conclusion is true and reason backward to the evidence

go back (verb)	regress (verb)
regain a former condition after a financial loss	go back to bad behavior
return in thought or speech to something	get worse or fall back to a previous condition
belong to an earlier time	go back to a previous state
	go back to a statistical means