payoff vs final payment

payoff and final payment both are nouns.

Word	Noun	Adjective	Verb	Adverb
payoff	Yes	No	No	No
final payment	Yes	No	No	No

As nouns, payoff and final payment are synonyms defined as:

payoff (noun)	final payment (noun)
a recompense for worthy acts or retribution for wrongdoing	the final payment of a debt
the final payment of a debt
payment made to a person in a position of trust to corrupt his judgment
the income or profit arising from such transactions as the sale of land or other property