turn back vs alter

turn back and alter both are verbs.

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

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

Other hypernyms of turn back include change, modify.

turn back (verb)	alter (verb)
go back to a previous state	remove the ovaries of
turn inside out or upside down	become different in some particular way, without permanently losing one's or its former characteristics or essence
hold back, as of a danger or an enemy; check the expansion or influence of	cause to change; make different; cause a transformation
retrace one's course	insert words into texts, often falsifying it thereby
force to go away; used both with concrete and metaphoric meanings	make an alteration to