trapezium n a quadrilateral with no parallel sides n a multiple star in the constellation of Orion n the wrist bone on the thumb side of the hand that articulates with the 1st and 2nd metacarpals Usage(s) He picked at a wall, found that it blocked a trapezium-shaped passageway 20 ft. Synonym(s) Trapezium trapezium bone os trapezium Antonym(s) parallelogram