regress vs turn back

regress is a noun but turn back is not a noun.

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

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

Other hypernyms of regress include regress, retrovert, return, revert.

As verbs, regress and turn back are synonyms defined as:

Other synonyms of regress include retrovert, return, revert.

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

regress (verb)	turn back (verb)
go back to bad behavior	go back to a previous state
get worse or fall back to a previous condition	turn inside out or upside down
go back to a previous state	hold back, as of a danger or an enemy; check the expansion or influence of
go back to a statistical means	retrace one's course
	force to go away; used both with concrete and metaphoric meanings