The Collaborative International Dictionary of English v.0.48:

Fenestration \Fen`es*tra"tion\, n.
   1. (Arch.) The arrangement and proportioning of windows; --
      used by modern writers for the decorating of an
      architectural composition by means of the window (and
      door) openings, their ornaments, and proportions.
      [1913 Webster]

   2. (Anat.) The state or condition of being fenestrated.
      [1913 Webster]

WordNet (r) 3.0 (2006):

fenestration
    n 1: the arrangement of windows in a building
    2: surgical procedure that creates a new fenestra to the cochlea
       in order to restore hearing lost because of osteosclerosis