Merriam-Webster Collegiate Dictionary - diagonal

 I. adjective  Etymology: Latin ~is, from Greek diagonios from angle to angle, from dia- + gonia angle; akin to Greek gony knee — more at knee  Date: 1563  1.  a. joining two vertices of a rectilinear figure that are nonadjacent or two vertices of a polyhedral figure that are not in the same face  b. passing through two nonadjacent edges of a polyhedron a ~ plane  2.  a. inclined obliquely from a reference line (as the vertical) wood with a ~ grain  b. having ~ markings or parts a ~ weave  II. noun  Date: 1571  1. a ~ straight line or plane  2.  a.  (1) a ~ direction  (2) a ~ row, arrangement, or pattern  b. something oriented in ~ position  3. slash 4