Varignon's theorem

Etymology
Named after French mathematician.

Proper noun

 * 1)  A statement in Euclidean geometry that deals with the construction of a particular parallelogram (the Varignon parallelogram) from an arbitrary quadrilateral.
 * 2)  A theorem stating that the torque of a resultant of two concurrent forces about any point is equal to the algebraic sum of the torques of its components about the same point.