Merriam-Webster Collegiate Dictionary - trapezium

 noun  (plural -ziums or trapezia)  Etymology: New Latin, from Greek trapezion, literally, small table, diminutive of trapeza table, from tra- four (akin to tettares four) + peza foot; akin to Greek pod-, pous foot — more at four, foot  Date: 1570  1.  a. a quadrilateral with no parallel sides  b. British trapezoid 1b  2. a bone in the wrist at the base of the metacarpal of the thumb