[plaque] n [F, fr. MF, metal sheet, fr. plaquier to plate, fr. MD placken to piece, patch; akin to MD placke piece, MHG placke patch] (1848) 1 a: an ornamental brooch; esp: the badge of an honorary order b: a flat thin piece (as of metal) used for decoration c: a commemorative or identifying inscribed tablet
2. a: a localized abnormal patch on a body part or surface b: a film of mucus that harbors bacteria on a tooth c: an atherosclerotic lesion d: a histopathologic lesion of brain tissue that is characteristic of Alzheimer's disease and consists of a cluster of degenerating nerve endings and dendrites around a core of amyloid
3: a clear area in a bacterial culture produced by destruction of cells by a virus