The Collaborative International Dictionary of English v.0.48:
Casemate \Case"mate\, n. [F. casemate, fr. It. casamatta, prob.
from casa house + matto, f. matta, mad, weak, feeble, dim.
from the same source as E. -mate in checkmate.]
1. (Fort.) A bombproof chamber, usually of masonry, in which
cannon may be placed, to be fired through embrasures; or
one capable of being used as a magazine, or for quartering
2. (Arch.) A hollow molding, chiefly in cornices.