The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. To light up; to decorate with artificial lights, as a
      building or city, in token of rejoicing or respect.
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   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.
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   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.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Illuminate \Il*lu"mi*nate\, v. i.
   To light up in token or rejoicing.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Illuminate \Il*lu"mi*nate\, a. [L. illuminatus, p. p.]
   Enlightened. --Bp. Hall.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Illuminate \Il*lu"mi*nate\, n.
   One who is enlightened; esp., a pretender to extraordinary
   light and knowledge.
   [1913 Webster]

WordNet (r) 3.0 (2006):

illuminate
    v 1: make lighter or brighter; "This lamp lightens the room a
         bit" [syn: light, illume, illumine, light up,
         illuminate]
    2: make free from confusion or ambiguity; make clear; "Could you
       clarify these remarks?"; "Clear up the question of who is at
       fault" [syn: clear, clear up, shed light on,
       crystallize, crystallise, crystalize, crystalise,
       straighten out, sort out, enlighten, illuminate,
       elucidate]
    3: add embellishments and paintings to (medieval manuscripts)