louver

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 […].

A series of sloping overlapping slats or boards which admit air and light but exclude rain etc.

Any of a system of slits, as in the hood of an automobile, for ventilation.