Lunette

Lunette (French diminutive of lune, moon), a crescent-shaped, semi-circular object. The term is particularly applied in architecture to a circular opening at the intersection of vaulting by a smaller vault, as in a ceiling for the entrance of light or in the lower stories of towers for the passage of bells. It is also used of a panel space of semi-circular shape, filled by a fresco or other decorative treatment. In fortification a “lunette” was originally an earthwork of half-moon shape; later it became a redan with short flanks, in trace somewhat resembling a bastion standing by itself without curtains on either side. The gorge was generally open.