The Collaborative International Dictionary of English v.0.48:

Plaque \Plaque\, n. [F. Cf. Plack, and see Placard.]
   Any flat, thin piece of metal, clay, ivory, or the like, used
   for ornament, or for painting pictures upon, as a slab,
   plate, dish, or the like, hung upon a wall; also, a smaller
   decoration worn on the person, as a brooch.
   [1913 Webster]

WordNet (r) 3.0 (2006):

plaque
    n 1: (pathology) a small abnormal patch on or inside the body
    2: a memorial made of brass [syn: brass, memorial tablet,
       plaque]