small change vs hard currency

small change and hard currency both are nouns.

Word	Noun	Adjective	Verb	Adverb
small change	Yes	No	No	No
hard currency	Yes	No	No	No

As nouns, hard currency is a hypernym of small change; that is, hard currency is a word with a broader meaning than small change:

Other hypernyms of small change include cash, hard cash.

small change (noun)	hard currency (noun)
a trifling sum of money	money in the form of bills or coins
	a currency that is not likely to depreciate suddenly in value