plaid, a long shawl or blanketlike outer wrap of woolen cloth, usually patterned in checks or tartan figures. Now a distinctive feature of the Highland costume, it was formerly worn in all parts of Scotland and in N England by both men and women. The early Celtic people excelled in dyeing and in Roman times wore gay, many-colored, checkered plaids, woven or sewed together in squares of different colors. Through the Middle Ages and until the 18th cent. the people of North Britain belted their plaids about them, the lower part forming the kilt, the upper part the cloak. A shepherd's plaid is of black-and-white check. A tartan plaid has crossbars of three or more colors combined in designs distinctive of the different Highland clans and serving a heraldic purpose. In modern usage plaid may signify merely pattern, as a plaid gingham.
See C. Hesketh, Tartans (1961); I. Grimble, Scottish Clans and Tartans (1982).