The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

         A casement of the great chamber window.  --Shak.
   [1913 Webster]

WordNet (r) 3.0 (2006):

casement
    n 1: a window sash that is hinged (usually on one side)

Moby Thesaurus II by Grady Ward, 1.0:

41 Moby Thesaurus words for "casement":
   bay, bay window, bow window, cadre, case, casement window, casing,
   chassis, doorframe, fabric, fan window, fanlight, frame, framework,
   framing, grille, lancet window, lantern, lattice, latticework,
   light, louver window, oriel, pane, picture frame, picture window,
   port, porthole, rose window, sash, shell, skeleton, skylight,
   transom, wicket, window, window bay, window case, window frame,
   window glass, windowpane



Easton's 1897 Bible Dictionary:

Casement
   a barrier of open-work placed before windows (Prov. 7:6). In
   Judg. 5:28 the Hebrew word is rendered "lattice," in the LXX.
   "network," an opening through which cool air is admitted.