Plaid
early 16th century: from Scottish Gaelic plaide ‘blanket’, of unknown ultimate origin.
wiktionary
From Scots plaid, of uncertain origin; perhaps from a past participle form of ply. Scottish Gaelic plaide(“blanket”) is probably a borrowing from Scots. [1]
Also compare Scottish Gaelic peall(“covering, veil, blanket”) << Latin pellis(“hide, covering”), but the OED finds the sound changes problematic. [2]
Alternative forms.
etymonline
plaid (n.)
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.
