Trapezium

·noun A bone of the carpus at the base of the first metacarpal, or thumb.

II. Trapezium ·noun A plane figure bounded by four right lines, of which no two are parallel.

III. Trapezium ·noun A region on the ventral side of the brain, either just back of the pons Varolii, or, as in man, covered by the posterior extension of its transverse fibers.