stopper vs stop up

stopper is a noun but stop up is not a noun.

Word	Noun	Adjective	Verb	Adverb
stopper	Yes	No	Yes	No
stop up	No	No	Yes	No

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

Other hypernyms of stopper include plug, secure.

stopper (noun)	stop up (noun)
blockage consisting of an object designed to fill a hole tightly
(bridge) a playing card with a value sufficiently high to insure taking a trick in a particular suit
an act so striking or impressive that the show must be delayed until the audience quiets down
a remark to which there is no polite conversational reply

stopper (verb)	stop up (verb)
close or secure with or as if with a stopper	fill or close tightly with or as if with a plug