underbody vs belly

underbody and belly both are nouns.

Word	Noun	Adjective	Verb	Adverb
underbody	Yes	No	No	No
belly	Yes	No	Yes	No

As nouns, belly is a hypernym of underbody; that is, belly is a word with a broader meaning than underbody:

underbody: the soft belly or underside of an animal's body
belly: the region of the body of a vertebrate between the thorax and the pelvis

Other hypernyms of underbody include abdomen, stomach, venter.

underbody (noun)	belly (noun)
the soft belly or underside of an animal's body	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

underbody (verb)	belly (verb)
	swell out or bulge out