IPA: /ˈkeɪs.meɪt/
KK: /ˈkeɪsˌmeɪt/
A strong, protected space used for military purposes, often to hold weapons or artillery, usually found in fortifications or on ships.
The soldiers took cover in the casemate during the battle.
Casemate is derived from the French word 'casemate' (meaning a chamber or room), which in turn comes from the Italian 'casamatta' (meaning a fortified room or chamber). The word refers to a fortified structure or chamber used for military purposes, typically to protect soldiers or equipment.
Think of a 'chamber' or 'room' that is 'fortified' for protection — that's what a casemate is.