fiat money vs paper money

fiat money and paper money both are nouns.

Word	Noun	Adjective	Verb	Adverb
fiat money	Yes	No	No	No
paper money	Yes	No	No	No

As nouns, paper money is a hypernym of fiat money; that is, paper money is a word with a broader meaning than fiat money:

fiat money: money that the government declares to be legal tender although it cannot be converted into standard specie
paper money: currency issued by a government or central bank and consisting of printed paper that can circulate as a substitute for specie

Other hypernyms of fiat money include folding money, paper currency.

fiat money (noun)	paper money (noun)
money that the government declares to be legal tender although it cannot be converted into standard specie	currency issued by a government or central bank and consisting of printed paper that can circulate as a substitute for specie