ready cash vs hard currency

ready cash and hard currency both are nouns.

Word	Noun	Adjective	Verb	Adverb
ready cash	Yes	No	No	No
hard currency	Yes	No	No	No

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

Other hypernyms of ready cash include cash, hard cash.

ready cash (noun)	hard currency (noun)
money in the form of cash that is readily available	money in the form of bills or coins
	a currency that is not likely to depreciate suddenly in value