arching aperture in a wall or concave ceiling. It may be crescent-shaped or semicircular. The word is the French diminutive of lune, “moon.” Lunettes may function as windows, they may form a cove for ornament or statuary, or they may be simply a section of wall framed by an arch or vault. In the last case, the area will sometimes be decorated with a mural.

The Basilica of Maxentius (Maxentius, Basilica of) (AD 310–313), in Rome, provides an early example of lunette windows, in the upper part of the nave over the aisle vaults. Giacomo da Vignola's Gesù church (1568–84), also in Rome, the prototype of many Baroque churches, features lunettes set into the base of the nave's barrel vault. In the 19th century lunettes were frequently used in large halls, either terminating wagon-headed ceilings or set into coves beneath a plane ceiling.