I. noun
also placque ˈplak chiefly Brit ˈplȧk
( -s )
Etymology: French, from Middle French, solid metal sheet, from plaquier to plate, from Middle Dutch placken to piece, spot, patch, beat; akin to Middle Dutch placke piece, spot, a coin, Middle High German placke spot, patch
1.
a. : an ornamental brooch ; especially : the badge of an honorary order
b. : a flat thin piece (as of metal, clay, or ivory) used for decoration (as on a wall or in an article of furniture)
a handsome ceramic plaque hung over the fireplace
c.
(1) : an inscribed usually metal tablet placed (as on a building or post) to identify a site or commemorate an individual or event
roadside plaques mark historic battles and gallant deeds of bygone days — Time
(2) : nameplate
d. : chip 5a
2. : an abnormal patch or flattened area on some body part or surface:
a. : a localized patch of skin disease
psoriatic plaque
b. : a deposit of lipoid or fibrous matter in the wall of a blood vessel
atheromatous plaques in the aorta
c. : a film of mucus harboring bacteria on a tooth
3. : blood platelet
II. noun
1. : a visibly distinct and especially a clear or opaque area in a bacterial culture produced by damage to or destruction of bacterial cells by a virus
2. : a histopathologic lesion of brain tissue that is characteristic of Alzheimer's disease and consists of a dense proteinaceous core composed primarily of beta-amyloid that is often surrounded and infiltrated by a cluster of degenerating axons and dendrites