prepay vs pay

prepay is not a noun while pay is a noun.

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

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

prepay (noun)	pay (noun)
	something that remunerates

prepay (verb)	pay (verb)
pay for something before receiving it	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