louver

noun

Etymology: Inherited from Middle English lover, from Old French lovier, lover (“skylight”), from Medieval Latin *lōdārium (attested as lōvārium), extension of lōdium, of unclear origin, but probably of Germanic origin and related to Frankish *laubijā (“shelter”).

1. A type of turret on the roof of certain medieval buildings designed to allow ventilation or the admission of light.

   “But darknesse dred and daily night did hover / Through all the inner parts, wherein they dwelt; / Ne lightned was with window, nor with lover, / But with continuall candle-light […].”

2. A series of sloping overlapping slats or boards which admit air and light but exclude rain etc.
3. Any of a system of slits, as in the hood of an automobile, for ventilation.