lunette

Concise Oxford English Dictionary © 2008 Oxford University Press:
lunette /luːˈnɛt/

▶noun

• 1 an arched aperture or window in a domed ceiling.

  ■ a crescent-shaped or semicircular alcove containing a painting or statue.

• 2 a fortification with two faces forming a projecting angle, and two flanks.

• 3 Christian Church a holder for the consecrated host in a monstrance.

• 4 a ring on a vehicle, by which it can be towed.

– origin C16 (denoting a semicircular horseshoe): from Fr., dimin. of lune ‘moon’, from L. luna.