Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
plaid (adj., n.), tartan (n.)
For purists the plaid is the right-angle-striped Scottish blanket worn over the shoulder and draped around the torso, the tartan a particular pattern for it. Today, for most Americans, plaid is the name of the pattern itself, tartan is the plaid-patterned cloth, usually a unique pattern adopted by a particular Scots clan; tartans are made into various garments, including plaids. Both senses are Standard.
