underbelly vs venter

underbelly and venter both are nouns.

Word	Noun	Adjective	Verb	Adverb
underbelly	Yes	No	No	No
venter	Yes	No	No	No

As nouns, venter is a hypernym of underbelly; that is, venter is a word with a broader meaning than underbelly:

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

Other hypernyms of underbelly include abdomen, belly, stomach.

underbelly (noun)	venter (noun)
the quality of being weak or unprotected	the region of the body of a vertebrate between the thorax and the pelvis
the soft belly or underside of an animal's body	a bulging body part (as the belly of a muscle)
lower side	the womb
	a speaker who expresses or gives vent to a personal opinion or grievance