rejoinder vs backtalk

rejoinder and backtalk both are nouns.

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

As nouns, backtalk is a hyponym of rejoinder; that is, backtalk is a word with a more specific, narrower meaning than rejoinder:

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

Other hyponyms of rejoinder include back talk, lip, mouth, sass, sassing.

rejoinder (noun)	backtalk (noun)
a quick reply to a question or remark (especially a witty or critical one)	an impudent or insolent rejoinder
(law) a pleading made by a defendant in response to the plaintiff's replication