bank bill vs greenback

bank bill and greenback both are nouns.

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

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

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

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

bank bill (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)