trapezium

noun

1. A four-sided polygon with two sides parallel

2. A four-sided polygon with no parallel sides and no sides equal; a simple convex irregular quadrilateral.

3. The trapezium bone of the wrist.

4. 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.