greenback vs Federal Reserve note

greenback and Federal Reserve note both are nouns.

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

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

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

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

greenback (noun)	Federal Reserve note (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)