fill up vs stop up

fill up and stop up both are verbs.

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

As verbs, stop up is a hyponym of fill up; that is, stop up is a word with a more specific, narrower meaning than fill up:

Other hyponyms of fill up include seal, plug, secure, coapt, conglutinate.

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