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Casement \Case"ment\, n. [Shortened fr. encasement. See {Incase 1st Case}, and cf. {Incasement}.] (Arch.) A window sash opening on hinges affixed to the upright side of the frame into which it is fitted. (Poetically) A window. A casement of the great chamber window. --Shak.
casement n : a window shash that is hinged (usually on one side)