pay up vs pay

pay up is not a noun while pay is a noun.

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

As verbs, pay up and pay are synonyms defined as:

Other synonyms of pay up include ante up.

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

pay up (noun)	pay (noun)
	something that remunerates

pay up (verb)	pay (verb)
cancel or discharge a debt	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