trapezium has 2 distinct synonyms spread across 1 of its 3 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. Its one recorded opposite is parallelogram.
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 quadrilateral with no parallel sides
a multiple star in the constellation of Orion
Synonyms, antonyms and the broader and narrower relations for trapezium come from Princeton University’s WordNet. Full sources and licences.
the wrist bone on the thumb side of the hand that articulates with the 1st and 2nd metacarpals