piece vs acicula

piece and acicula both are nouns.

Word	Noun	Adjective	Verb	Adverb
piece	Yes	No	Yes	No
acicula	Yes	No	No	No

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

piece: a portion of a natural object
acicula: a needlelike part or structure of a plant or animal or crystal; as a spine or bristle or crystal

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

piece (noun)	acicula (noun)
a separate part of a whole	a needlelike part or structure of a plant or animal or crystal; as a spine or bristle or crystal
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)	acicula (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