rectum vs body part

rectum and body part both are nouns.

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

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

rectum: the terminal section of the alimentary canal; from the sigmoid flexure to the anus
body part: any part of an organism such as an organ or extremity

rectum (noun)	body part (noun)
the terminal section of the alimentary canal; from the sigmoid flexure to the anus	any part of an organism such as an organ or extremity