return vs turn back

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

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

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

Other synonyms of return include regress, retrovert, revert.

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

return: go or come back to place, condition, or activity where one has been before
turn back: retrace one's course

return (noun)	turn back (noun)
the act of going back to a prior location
a coming to or returning home
getting something back again
a tennis stroke that sends the ball back to the other player
(American football) the act of running back the ball after a kickoff or punt or interception or fumble
a reciprocal group action
the act of someone appearing again
the key on electric typewriters or computer keyboards that causes a carriage return and a line feed
document giving the tax collector information about the taxpayer's tax liability
a quick reply to a question or remark (especially a witty or critical one)
happening again (especially at regular intervals)
the occurrence of a change in direction back in the opposite direction
the income or profit arising from such transactions as the sale of land or other property

return (verb)	turn back (verb)
go back to a previous state	go back to a previous state
be restored	turn inside out or upside down
go back to something earlier	hold back, as of a danger or an enemy; check the expansion or influence of
answer back	retrace one's course
submit (a report, etc.) to someone in authority	force to go away; used both with concrete and metaphoric meanings
pass down
make a return
give or supply
go or come back to place, condition, or activity where one has been before
return to a previous position; in mathematics
bring back to the point of departure
pay back
return in kind
give back
be inherited by
elect again