noun

1. an open turret or lantern on the roof of a medieval building
2. 1. a window or opening furnished with a series of overlapping, horizontal slats arranged so as to admit light and air but shed rain water outward
   2. any of these slats
      also louver board
   3. any similar arrangement of slats or fins, often adjustable, used to control ventilation, light intensity, etc.
3. a ventilating slit

Etymology: ME luver < MFr lover < MDu love, gallery (in a theater), akin to OHG louba: see lodge