shoulder has 3 distinct synonyms spread across 2 of its 8 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.
the part of the body between the neck and the upper arm
a cut of meat including the upper joint of the foreleg
a ball-and-socket joint between the head of the humerus and a cavity of the scapula
the part of a garment that covers or fits over the shoulder
“an ornamental gold braid on the shoulder of his uniform”
a narrow edge of land (usually unpaved) along the side of a road
“the car pulled off onto the shoulder”
Synonyms, antonyms and the broader and narrower relations for shoulder come from Princeton University’s WordNet. Full sources and licences.