The Collaborative International Dictionary of English v.0.48:

Illumination \Il*lu`mi*na"tion\, n. [L. illuminatio: cf. F.
   illumination.]
   1. The act of illuminating, or supplying with light; the
      state of being illuminated.
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   2. Festive decoration of houses or buildings with lights.
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   3. Adornment of books and manuscripts with colored
      illustrations. See Illuminate, v. t., 3.
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   4. That which is illuminated, as a house; also, an ornamented
      book or manuscript.
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   5. That which illuminates or gives light; brightness;
      splendor; especially, intellectual light or knowledge.
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            The illumination which a bright genius giveth to his
            work.                                 --Felton.
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   6. (Theol.) The special communication of knowledge to the
      mind by God; inspiration.
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            Hymns and psalms . . . are framed by meditation
            beforehand, or by prophetical illumination are
            inspired.                             --Hooker.
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WordNet (r) 3.0 (2006):

illumination
    n 1: a condition of spiritual awareness; divine illumination;
         "follow God's light" [syn: light, illumination]
    2: the degree of visibility of your environment
    3: an interpretation that removes obstacles to understanding;
       "the professor's clarification helped her to understand the
       textbook" [syn: clarification, elucidation,
       illumination]
    4: the luminous flux incident on a unit area [syn:
       illuminance, illumination]
    5: painting or drawing included in a book (especially in
       illuminated medieval manuscripts) [syn: miniature,
       illumination]