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