A plaid is a long shawl or scarf- some twelve yards of narrow cloth wrapped round the waist, or over the chest and one shoulder, and reaching to the knees. It may be chequered or not, but the English use of the word in such a compound a Scotch-plaids, meaning chequered cloth, is a blunder for Scotch tartans. The tartan is the chequered pattern, every clan having its own tartan. A tartanplaid is a Scotch scarf of a tartan or checked pattern.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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