plaque

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A flat plate, slab, or disk that is ornamented or engraved for mounting, as on a wall for decoration or on a monument for information.
• noun A small pin or brooch worn as an ornament or a badge of membership.
• noun A deposit of fatty material on the inner lining of an arterial wall, characteristic of atherosclerosis.
• noun A scaly patch on a body part, especially the skin.
• noun A film of mucus and bacteria on a tooth surface.
• noun A lesion found in the brain tissue of people with Alzheimer's disease, consisting mainly of beta-amyloid protein and degenerating nerve tissue.
• noun A sharply defined zone of demyelination in the brain characteristic of multiple sclerosis.
• noun A clear, often round patch of lysed cells in an otherwise opaque layer of a bacteria or cell culture.

from The Century Dictionary.

• noun An ornamental plate; a brooch; the plate of a clasp.
• noun A square, oblong, or circular tablet of bronze or silver, the largest dimension of which extends to three or four inches, ornamented in relief with some religious, mythological, allegorical, or decorative subject.
• noun Any tablet or distinctly flat plate of metal or porcelain, whether plain or ornamented; partieularly. an ornamental circular plate intended for a wall-decoration. See cut in next column.
• noun The especial decoration of a high rank in many honorary orders. See star, insignia, order, 6 .
• noun In anatomy and zoology, a small flat object of round figure, as a blood-disk; a little plate. Also plaquette
• noun A patch.
• noun A billon or silver coin current in the fourteenth and fifteenth centuries in Brabant, Liège, Lorraine, and France.

from the GNU version of the Collaborative International Dictionary of English.

• noun 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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun 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.
• noun uncountable An accumulation of biofilm, or bacteria on teeth.
• noun uncountable, medicine Atheroma, an accumulation in artery walls made up of macrophage cells and debris containing lipids, (cholesterol and fatty acids), calcium, and connective tissue.
• noun biology A clearing in a bacterial lawn caused by a virus.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (pathology) a small abnormal patch on or inside the body
• noun a memorial made of brass