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1848, "ornamental plate or tablet," from French plaque "metal plate, coin" (15c.), perhaps through Flemish placke "small coin," from Middle Dutch placke "disk, patch, stain," related to German Placken "spot, patch" (cf. placard). Meaning "deposit on walls of arteries" is first attested 1891; that of "bacteria deposits on teeth" is 1898.
A small disk-shaped formation or growth; a patch.
A deposit of fatty material on the inner lining of an arterial wall, characteristic of atherosclerosis.
A clear, often round patch of lysed cells in an otherwise opaque layer of a bacteria or cell culture.
A scaly patch formed on the skin by psoriasis.
A sharply defined zone of demyelination characteristic of multiple sclerosis.