trapezium

(geometry, Britain, Australia, New Zealand) A four-sided polygon with two sides parallel

(geometry, US, dated) A four-sided polygon with no parallel sides and no sides equal; a simple convex irregular quadrilateral.

(anatomy) The trapezium bone of the wrist.

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.