underbelly vs underbody

underbelly and underbody both are nouns.

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

As nouns, underbelly and underbody are synonyms defined as:

underbelly and underbody: the soft belly or underside of an animal's body

underbelly (noun)	underbody (noun)
the quality of being weak or unprotected	the soft belly or underside of an animal's body
the soft belly or underside of an animal's body
lower side