Definition of "Diagonal" :

noun: a punctuation mark (/) used to separate related items of information

noun: (mathematics) a set of entries in a square matrix running diagonally either from the upper left to lower right entry or running from the upper right to lower left entry

noun: an oblique line of squares of the same color on a checkerboard

"The bishop moves on the diagonals."

noun: a line or cut across a fabric that is not at right angles to a side of the fabric

noun: (geometry) a straight line connecting any two vertices of a polygon that are not adjacent

adjective: having an oblique or slanted direction

adjective: connecting two nonadjacent corners of a plane figure or any two corners of a solid that are not in the same face

"A diagonal line across the page."