piece vs body part

piece and body part both are nouns.

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

As nouns, body part is a hyponym of piece; that is, body part is a word with a more specific, narrower meaning than piece:

Other hyponyms of piece include corpus, acicula, base, corner, craton, cutting, fragment, hunk, lump, nub, stub, segment, slice, strip, world.

piece (noun)	body part (noun)
a separate part of a whole	any part of an organism such as an organ or extremity
game equipment consisting of an object used in playing certain board games
a portable gun
a work of art of some artistic value
an item that is an instance of some type
a distance
a musical work that has been created
an artistic or literary composition
an instance of some kind
a serving that has been cut from a larger portion
a portion of a natural object
a share of something
a period of indeterminate length (usually short) marked by some action or condition

piece (verb)	body part (verb)
repair by adding pieces
eat intermittently; take small bites of
join during spinning
to join or unite the pieces of
create by putting components or members together