bank note vs greenback

bank note and greenback both are nouns.

Word	Noun	Adjective	Verb	Adverb
bank note	Yes	No	No	No
greenback	Yes	No	No	No

As nouns, bank note and greenback are synonyms defined as:

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

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

bank note (noun)	greenback (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)