1.(geometry) a straight line connecting any two vertices of a polygon that are not adjacent
2.a line or cut across a fabric that is not at right angles to a side of the fabric
3.an oblique line of squares of the same color on a checkerboard;
the bishop moves on the diagonals
4.(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
5.a punctuation mark (/) used to separate related items of information
6.at an angle; especially 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
7.having an oblique or slanted direction