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]

Moby Thesaurus II by Grady Ward, 1.0:

59 Moby Thesaurus words for "skylight":
   afterglow, air glow, bay, bay window, bow window, candescence,
   casement, casement window, ceiling, eaves, fan window, fanlight,
   flush, gleam, glint, gloss, glow, grille, housetop, incandescence,
   lancet window, lantern, lattice, light, louver window, luster,
   oriel, overhead, pane, penthouse, picture window, plafond, port,
   porthole, ridgepole, roof, roof garden, roof-deck, roofage,
   roofing, roofpole, rooftop, rooftree, rose window, sheen, shine,
   shingles, shininess, shining light, slates, sunset glow, tiles,
   top, transom, wicket, window, window bay, window glass,
   windowpane