backtalk vs comeback

backtalk and comeback both are nouns.

Word	Noun	Adjective	Verb	Adverb
backtalk	Yes	No	No	No
comeback	Yes	No	No	No

As nouns, comeback is a hypernym of backtalk; that is, comeback is a word with a broader meaning than backtalk:

backtalk: an impudent or insolent rejoinder
comeback: a quick reply to a question or remark (especially a witty or critical one)

Other hypernyms of backtalk include counter, rejoinder, replication, retort, return, riposte.

backtalk (noun)	comeback (noun)
an impudent or insolent rejoinder	return by a celebrity to some previously successful activity
	a quick reply to a question or remark (especially a witty or critical one)