bank note vs paper currency

bank note and paper currency both are nouns.

Word	Noun	Adjective	Verb	Adverb
bank note	Yes	No	No	No
paper currency	Yes	No	No	No

As nouns, paper currency is a hypernym of bank note; that is, paper currency is a word with a broader meaning than bank note:

bank note: a piece of paper money (especially one issued by a central bank)
paper currency: currency issued by a government or central bank and consisting of printed paper that can circulate as a substitute for specie

Other hypernyms of bank note include folding money, paper money.

bank note (noun)	paper currency (noun)
a piece of paper money (especially one issued by a central bank)	currency issued by a government or central bank and consisting of printed paper that can circulate as a substitute for specie