The Collaborative International Dictionary of English v.0.48:

Skylight \Sky"light`\, n.
   A window placed in the roof of a building, in the ceiling of
   a room, or in the deck of a ship, for the admission of light
   from above.
   [1913 Webster]

WordNet (r) 3.0 (2006):

skylight
    n 1: a window in a roof to admit daylight [syn: skylight,
         fanlight]