plaque (n.)

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" (compare placard). Meaning "deposit on walls of arteries" is attested by 1891; that of "bacteria deposits on teeth" is by 1898.