turn back vs lapse

turn back is not a noun while lapse is a noun.

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

As verbs, lapse is a hyponym of turn back; that is, lapse is a word with a more specific, narrower meaning than turn back:

Other hyponyms of turn back include fall back, recidivate, regress, relapse, retrogress, resile, go back, recover, recuperate.

turn back (noun)	lapse (noun)
	a mistake resulting from inattention
	a failure to maintain a higher state
	a break or intermission in the occurrence of something

turn back (verb)	lapse (verb)
go back to a previous state	go back to bad behavior
turn inside out or upside down	drop to a lower level, as in one's morals or standards
hold back, as of a danger or an enemy; check the expansion or influence of	end, at least for a long time
retrace one's course	for time to move forward
force to go away; used both with concrete and metaphoric meanings	pass into a specified state or condition; sink into
	let slip