In geometry, extending, as a line, from one angle to another not adjacent, within any figure.Being in an oblique direction; lying obliquely.Marked by oblique lines: as, diagonal cloth..A soft material used as a ground for embroidery, generally made very wide, and dyed in plain colors without pattern.A material for men's wear, especially for coats and waistcoats.n. A straight line drawn from one angle to or through another, not adjacent, in any plane or solid figure.n. Any oblique line.n. Specificallyn. In chess, checkers, etc., a line of squares running diagonally across the board. See chess.n. Same as diagonal cloth, especially in the United States: a term introduced about 1875.