- extending between the vertices of any two nonadjacent angles in a polygonal figure or between any two vertices not in the same face in a polyhedral figure
- moving or extending obliquely, esp. at a 45° angle; slanting
- having slanting markings, lines, etc.

Origin of diagonal

Classical Latin*diagonalis*from Classical Greek

*diag?nios*from

*dia-*, through +

*g?nia*, an angle, corner: see knee

- a diagonal line or plane
- virgule

- any diagonal course, row, order, or part
- cloth woven with diagonal lines; twill