swell up vs belly

swell up is not a noun while belly is a noun.

Word	Noun	Adjective	Verb	Adverb
swell up	No	No	Yes	No
belly	Yes	No	Yes	No

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

Other hyponyms of swell up include distend, belly out, blow up, puff, puff out, puff up, bloat, blister, vesicate.

swell up (noun)	belly (noun)
	the underpart of the body of certain vertebrates such as snakes or fish
	the region of the body of a vertebrate between the thorax and the pelvis
	a protruding abdomen
	the hollow inside of something
	a part that bulges deeply

swell up (verb)	belly (verb)
expand abnormally	swell out or bulge out