pay cash vs pay

pay cash is not a noun while pay is a noun.

Word	Noun	Adjective	Verb	Adverb
pay cash	No	No	Yes	No
pay	Yes	No	Yes	No

As verbs, pay is a hypernym of pay cash; that is, pay is a word with a broader meaning than pay cash:

pay cash (noun)	pay (noun)
	something that remunerates

pay cash (verb)	pay (verb)
pay (for something) with cash	dedicate
	bear (a cost or penalty), in recompense for some action
	convey, as of a compliment, regards, attention, etc.; bestow
	give money, usually in exchange for goods or services
	bring in
	do or give something to somebody in return
	cancel or discharge a debt
	make a compensation for
	discharge or settle
	render
	be worth it