The Collaborative International Dictionary of English v.0.48:

Louver \Lou"ver\, Louvre \Lou"vre\, n. [OE. lover, OF. lover,
   lovier; or l'ouvert the opening, fr. overt, ouvert, p. p. of
   ovrir, ouvrir, to open, F. ouvrir. Cf. Overt.] (Arch.)
   A small lantern. See Lantern, 2
   (a) . [Written also lover, loover, lovery, and
       luffer.]

   2. Same as louver boards, below
      [PJC]

   3. A set of slats resembling louver boards, arranged in a
      vertical row and attached at each slat end to a frame
      inserted in or part of a door or window; the slats may be
      made of wood, plastic, or metal, and the angle of
      inclination of the slats may be adjustable simultaneously,
      to allow more or less light or air into the enclosure.
      [PJC]

   Louver boards or Louver boarding, the sloping boards set
      to shed rainwater outward in openings which are to be left
      otherwise unfilled; as belfry windows, the openings of a
      louver, etc.

   Louver work, slatted work.