fanny vs body part

fanny and body part both are nouns.

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

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

fanny (noun)	body part (noun)
the fleshy part of the human body that you sit on	any part of an organism such as an organ or extremity
external female sex organs