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c.1200, "short, loose, sleeveless cloak," variant of mantle (q.v.). Sense of "movable shelter for soldiers besieging a fort" is from 1520s. Meaning "timber or stone supporting masonry above a fireplace" first recorded 1510s, a shortened form of Middle English mantiltre "mantletree" (late 15c.).
hood or other similar projection, usually ornamented, that surrounds the opening of a fireplace and directs smoke up to the chimney flue. See chimneypiece.