Lunette

noun

1. A small opening in a vaulted roof of a circular or crescent shape.
2. A crescent-shaped recess or void in the space above a window or door.
3. An image or other representation of a crescent moon.
4. (fortifications) A field work consisting of two projecting faces forming a wedge each of which extends from one of two parallel flanks.
5. A luna: a crescent-shaped receptacle, often glass, for holding the (consecrated) host (the bread of communion) upright when exposed in the monstrance.