piece has 22 distinct synonyms spread across 14 of its 18 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
a separate part of a whole
“an important piece of the evidence”
a musical work that has been created
“the composition is written in four movements”
a portable gun
“he wore his firearm in a shoulder holster”
a distance
“it is down the road a piece”
a work of art of some artistic value
“this store sells only objets d'art”
create by putting components or members together
“She pieced a quilt”
join during spinning
“piece the broken pieces of thread, slivers, and rovings”
Synonyms, antonyms and the broader and narrower relations for piece come from Princeton University’s WordNet. Full sources and licences.