What is the meaning of diagonal?

noun

• Geometry) a straight line connecting any two vertices of a polygon that are not adjacent. (
• A line or cut across a fabric that is not at right angles to a side of the fabric.
  • synonyms: bias
• An oblique line of squares of the same color on a checkerboard.
  • usage: "the bishop moves on the diagonals"
• 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. (
• A punctuation mark (/) used to separate related items of information.
  • synonyms: solidus, slash, virgule, stroke, separatrix

adjective

• Connecting two nonadjacent corners of a plane figure or any two corners of a solid that are not in the same face.
  • usage: "a diagonal line across the page"
• Having an oblique or slanted direction.
  • synonyms: aslant, aslope, slanted, slanting, sloped, sloping