Emily Dickinson Lexicon

CASE'-MATE, n. [Fr. casemate; It. casamatta; Sp. and Port. casamata; from casa, a house.]

1. In fortification, a vault of mason's work in the flank of a bastion, next to the curtain, somewhat inclined toward the capital of the bastion, serving as a battery to defend the face of the opposite bastion, and the moat or ditch. – Chambers.
2. A well, with its subterraneous branches, dug in the passage of the bastion, till the miner is heard at work, and air given to the mine. – Harris.