The Collaborative International Dictionary of English v.0.48:

Illustrate \Il*lus"trate\, v. t. [imp. & p. p. Illustrated; p.
   pr. & vb. n. Illustrating.] [L. illustratus, p. p. of
   illustrare to illustrate, fr. illustris bright. See
   Illustrious.]
   1. To make clear, bright, or luminous.
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            Here, when the moon illustrates all the sky.
                                                  --Chapman.
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   2. To set in a clear light; to exhibit distinctly or
      conspicuously. --Shak.
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            To prove him, and illustrate his high worth.
                                                  --Milton.
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   3. To make clear, intelligible, or apprehensible; to
      elucidate, explain, or exemplify, as by means of figures,
      comparisons, and examples.
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   4. To adorn with pictures, as a book or a subject; to
      elucidate with pictures, as a history or a romance.
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   5. To give renown or honor to; to make illustrious; to
      glorify. [Obs.]
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            Matter to me of glory, whom their hate
            Illustrates.                          --Milton.
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The Collaborative International Dictionary of English v.0.48:

Illustrate \Il*lus"trate\, a. [L. illustratus, p. p.]
   Illustrated; distinguished; illustrious. [Obs.]
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         This most gallant, illustrate, and learned gentleman.
                                                  --Shak.
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WordNet (r) 3.0 (2006):

illustrate
    v 1: clarify by giving an example of [syn: exemplify,
         illustrate, instance]
    2: depict with an illustration
    3: supply with illustrations; "illustrate a book with drawings"