1510s, "garment consisting of a long piece of woolen cloth, often having a tartan pattern, traditionally worn in Scotland," from Scottish, from or related to Gaelic plaide "blanket, mantle," a word of uncertain etymology, perhaps a contraction of peallaid "sheepskin," from peall "skin," from Latin pellis (but OED finds this "phonetically improbable").
It is a large rectangular piece of woolen stuff, and is worn in Scotland by both sexes for warmth and for protection against the weather. It is a special dress of the Highlanders, and forms part of the uniform of certain infantry regiments in the British army. A variety of the plaid is called maud. [Century Dictionary]
The wearing of it by males was forbidden by Act of Parliament, under penalty of transportation, 1746-82. The meaning "a pattern of bars crossing each other at right angles" is by 1890. As an adjective, "ornamented with a pattern of bars or stripes of color crossing one another at right angles," c. 1600, from the noun.