DIAGONAL, adjective [Gr. A corner.]
1. In geometry, extending from one angle to another of a quadrilateral figure, and dividing it into two equal parts.
2. Being in an angular direction.
DIAGONAL, noun A right line drawn from angle to angle of a quadrilateral figure, as a square or parallelogram, and dividing it into two equal parts. It is sometimes called the diameter, and sometimes the diametral.