·noun A member, in a framed structure, running obliquely across a panel.
II. Diagonal ·noun A diagonal cloth; a kind of cloth having diagonal stripes, ridges, or welts made in the weaving.
III. Diagonal ·noun A right line drawn from one angle to another not adjacent, of a figure of four or more sides, and dividing it into two parts.
IV. Diagonal ·adj Joining two not adjacent angles of a quadrilateral or multilateral figure; running across from corner to corner; crossing at an angle with one of the sides.