a. Pertaining to a decagon; having ten sides.

a. [ L. diagonalis, fr. Gr. &unr_; from to angle; dia` through + &unr_; an angle; perh. akin to E. knee: cf. F. diagonal. ] (Geom.) 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. [ 1913 Webster ]

Diagonal bond (Masonry), herringbone work. See Herringbone, a. --
Diagonal built (Shipbuilding), built by forming the outer skin of two layers of planking, making angles of about 45° with the keel, in opposite directions. --
Diagonal cleavage. See under Cleavage. --
Diagonal molding (Arch.), a chevron or zigzag molding. --
Diagonal rib. (Arch.) See Cross-springer. --
Diagonal scale, a scale which consists of a set of parallel lines, with other lines crossing them obliquely, so that their intersections furnish smaller subdivisions of the unit of measure than could be conveniently marked on a plain scale. --
Diagonal stratification. (Geol.) Same as Cross bedding, under Cross, a. [ 1913 Webster ]

n. 1. 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. [ 1913 Webster ]

2. (Engin.) A member, in a framed structure, running obliquely across a panel. [ 1913 Webster ]

3. A diagonal cloth; a kind of cloth having diagonal stripes, ridges, or welts made in the weaving. [ 1913 Webster ]

adj. (Math.) able to be diagonalized; -- of a matrix. [ PJC ]

v. t. (Math.) to transform a matrix to a diagonal matrix. [ WordNet 1.5 ]

adv. In a diagonal direction. [ 1913 Webster ]