greenback vs banknote

greenback and banknote both are nouns.

Word	Noun	Adjective	Verb	Adverb
greenback	Yes	No	No	No
banknote	Yes	No	No	No

As nouns, greenback and banknote are synonyms defined as:

greenback and banknote: a piece of paper money (especially one issued by a central bank)

Other synonyms of greenback include bank bill, bank note, banker's bill, bill, Federal Reserve note, government note, note.

greenback (noun)	banknote (noun)
a piece of paper money (especially one issued by a central bank)	a piece of paper money (especially one issued by a central bank)