hard currency vs hard cash

hard currency and hard cash both are nouns.

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

As nouns, hard currency and hard cash are synonyms defined as:

Other synonyms of hard currency include cash.

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