noun

• (countable) Any flat, thin piece of clay, ivory, metal, etc., used for ornament, or for painting pictures upon, as a dish, plate, slab, etc., hung upon a wall; also, a smaller decoration worn by a person, such as a brooch.
• (countable) A piece of flat metal with writing on it, attached to a building, monument, or other structure to remind people of a person or an event.
• (countable) A small card representing an amount of money, used for betting in casinos; a sort of gaming chip.
• (countable, biology) A clearing in a bacterial lawn caused by a virus.
• (countable, music) In the Hornbostel–Sachs classification system: any flat, thin musical instrument.
• (countable, pathology) A broad patch of abnormal tissue distinguishable from surrounding tissue, especially a broad papule (“inflamed, irritated patch”) on the skin.
• (countable, uncountable, pathology) An abnormal accumulation of material in or on an organ of the body, often associated with disease.
• (countable, uncountable, pathology) An accumulation in artery walls made up of macrophage cells and debris containing lipids, (cholesterol and fatty acids), calcium, and connective tissue; an atheroma.
• (uncountable, dentistry) An accumulation of biofilm, or bacteria, on teeth, which may develop into dental calculus (tartar).
• (countable, medicine) A deposit of beta-amyloid protein occurring in a nerve cell and associated with Alzheimer's disease.