E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
A plaid is a long shawl or scarfsome 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 as Scotch-plaids, meaning chequered cloth, is a blunder for Scotch tartans. The tartan is the chequered pattern, every clan having its own tartan. A tartan-plaid is a Scotch scarf of a tartan or checked pattern.