diagonal (Adjective) — Connecting two nonadjacent corners of a plane figure or any two corners of a solid that are not in the same face. ex. "a diagonal line across the page"
diagonal (Adjective) — Having an oblique or slanted direction.
diagonal (Noun) — (geometry) a straight line connecting any two vertices of a polygon that are not adjacent.
diagonal (Noun) — A line or cut across a fabric that is not at right angles to a side of the fabric.
diagonal (Noun) — An oblique line of squares of the same colour on a checkerboard. ex. "the bishop moves on the diagonals"
diagonal (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.
diagonal (Noun) — A punctuation mark (/) used to separate related items of information.