Louver

(lōō'vər), n. [Fr. l'ouvert, the opening, properly p. p. of ouvrir, to open, O. Fr. doerir, auerir, Pr. obrir, abrir, adubrir, from Lat. deoperire, with d prefixed, from operire, to cover, to shut; but Sp. abrir, It. aprire, from Lat. aperire, to open.] An opening in the roof of ancient buildings for the escape of smoke or for ventilation, often in the form of a turret or small lantern. [Written also lover, loover, lorey, and luffer.] Oxf. Gloss.

Louver or luffer boarding, the sloping boards of a tower window, as in church towers.—Louver window (Arch.), an opening in a bell-tower or church steeple, crossed by a series of slats or sloping boards, to exclude rain, but allow the passage of sound from the bells.—Louver work, slatted work.