The Collaborative International Dictionary of English v.0.48:

Luminary \Lu"mi*na*ry\, n.; pl. Luminaries, [F. luminaire, L.
   luminare a light or lamp, which was lighted in the churches,
   a luminary, fr. lumen, luminis, light, fr. lucere to be
   light, to shine, lux, lucis, light. See Light.]
   [1913 Webster]
   1. Any body that gives light, especially one of the heavenly
      bodies. " Radiant luminary." --Skelton.
      [1913 Webster]

            Where the great luminary . . .
            Dispenses light from far.             --Milton.
      [1913 Webster]

   2. One who illustrates any subject, or enlightens mankind;
      as, Newton was a distinguished luminary.
      [1913 Webster]

WordNet (r) 3.0 (2006):

luminary
    n 1: a celebrity who is an inspiration to others; "he was host
         to a large gathering of luminaries" [syn: luminary,
         leading light, guiding light, notable, notability]

The Devil's Dictionary (1881-1906):

LUMINARY, n.  One who throws light upon a subject; as an editor by not
writing about it.