[di.ag.o.nal] adj [L diagonalis, fr. Gk diagonios from angle to angle, fr. dia- + gonia angle; akin to Gk gony knee--more at knee] (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 diagonal markings or parts "a ~ weave"
diagonal n (1571) 1: a diagonal straight line or plane
2. a (1): a diagonal direction (2): a diagonal row, arrangement, or pattern b: something oriented in diagonal position
3: a mark / used typically to denote "or" (as in and/or), "and or" (as in straggler/deserter), or "per" (as in feet/second)--called also solidus, virgule -- on the diagonal : in an oblique direction: diagonally