small change vs hard cash

small change and hard cash both are nouns.

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

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

Other hypernyms of small change include cash, hard currency.

small change (noun)	hard cash (noun)
a trifling sum of money	money in the form of bills or coins