stop up vs fill up

stop up and fill up both are verbs.

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

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

Other hypernyms of stop up include close.

stop up (verb)	fill up (verb)
fill or close tightly with or as if with a plug	make full, also in a metaphorical sense
	become full
	eat until one is sated
	fill or stop up