Federal Reserve note vs greenback

Federal Reserve note and greenback both are nouns.

Word	Noun	Adjective	Verb	Adverb
Federal Reserve note	Yes	No	No	No
greenback	Yes	No	No	No

As nouns, Federal Reserve note and greenback are synonyms defined as:

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

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

Federal Reserve 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)