belly vs body part

belly and body part both are nouns.

Word	Noun	Adjective	Verb	Adverb
belly	Yes	No	Yes	No
body part	Yes	No	No	No

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

belly: the region of the body of a vertebrate between the thorax and the pelvis
body part: any part of an organism such as an organ or extremity

belly (noun)	body part (noun)
the underpart of the body of certain vertebrates such as snakes or fish	any part of an organism such as an organ or extremity
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

belly (verb)	body part (verb)
swell out or bulge out