Mathematics .

connecting two nonadjacent angles or vertices of a polygon or polyhedron, as a straight line.

extending from one edge of a solid figure to an opposite edge, as a plane.

having an oblique direction.

having oblique lines, ridges, markings, etc.

a diagonal line or plane.

virgule.

a diagonal row, part, pattern, etc.

Manège . (of a horse at a trot) the foreleg and the hind leg, diagonally opposite, which move forward simultaneously.

diagonal cloth.

Mathematics . a set of entries in a square matrix running either from upper left to lower right (main diagonal or principal diagonal) or lower left to upper right (secondary diagonal).

Chess . one of the oblique lines of squares on a chessboard

He advanced his bishop along the open diagonal.

adjective

askew , bevel , beveled , bias , biased , cater-cornered , catty-cornered , cornerways , cross , crossways , crosswise , inclining , kitty-cornered , oblique , skewing , slanted , slanting , transversal , transverse , angled , catercorner , catercornered