paying back vs revenge

paying back and revenge both are nouns.

Word	Noun	Adjective	Verb	Adverb
paying back	Yes	No	No	No
revenge	Yes	No	Yes	No

As nouns, revenge is a hyponym of paying back; that is, revenge is a word with a more specific, narrower meaning than paying back:

Other hyponyms of paying back include payment, requital, retaliation, reciprocation, tit for tat.

paying back (noun)	revenge (noun)
a reciprocal group action	action taken in return for an injury or offense

paying back (verb)	revenge (verb)
	take revenge for a perceived wrong