/plak/ , n.
1. a thin, flat plate or tablet of metal, porcelain, etc., intended for ornament, as on a wall, or set in a piece of furniture.
2. an inscribed commemorative tablet, usually of metal placed on a building, monument, or the like.
3. a platelike brooch or ornament, esp. one worn as the badge of an honorary order.
4. Anat. , Pathol. a flat, often raised, patch on the skin or other organ, as on the inner lining of arterial walls in atherosclerosis.
5. Dentistry. a soft, sticky, whitish matlike film attached to tooth surfaces, formed largely by the growth of bacteria that colonize the teeth.
6. Bacteriol. a cleared region in a bacterial culture, resulting from lysis of bacteria by bacteriophages.
[ 1840-50; plaquer to plate placken to patch; cf. PLACKET ]