Source : Webster's Revised Unabridged Dictionary (1913)

Illuminating \Il*lu"mi*na`ting\, a.
   Giving or producing light; used for illumination.

   {Illuminating gas}. See {Gas}, n., 2
   (a) .

Illuminate \Il*lu"mi*nate\, v. t. [imp. & p. p. {Illuminated};
   p. pr. & vb. n. {Illuminating}.] [L. illuminatus, p. p. of
   illuminare; pref. il- in + luminare to enlighten, fr. lumen
   light. See {Luminous}, and cf. {Illume}, {Illumine},
   {Enlimn}, {Limn}.]
   1. To make light; to throw light on; to supply with light,
      literally or figuratively; to brighten.

   2. To light up; to decorate with artificial lights, as a
      building or city, in token of rejoicing or respect.

   3. To adorn, as a book or page with borders, initial letters,
      or miniature pictures in colors and gold, as was done in
      manuscripts of the Middle Ages.

   4. To make plain or clear; to dispel the obscurity to by
      knowledge or reason; to explain; to elucidate; as, to
      illuminate a text, a problem, or a duty.

Source : WordNet®

illuminating
     adj 1: highly enlightening; making understandable or clarifying;
            "an illuminating lecture"; "illuminating pieces of
            information" [syn: {enlightening}] [ant: {unilluminating}]
     2: providing light; "the sun's illuminating rays"