come back vs retort

come back is not a noun while retort is a noun.

Word	Noun	Adjective	Verb	Adverb
come back	No	No	Yes	No
retort	Yes	No	Yes	No

As verbs, come back and retort are synonyms defined as:

Other synonyms of come back include rejoin, repay, return, riposte.

come back (noun)	retort (noun)
	a vessel where substances are distilled or decomposed by heat
	a quick reply to a question or remark (especially a witty or critical one)