1. To make clear, bright, or luminous. Here, when the moon illustrates all the sky. (Chapman)
2. To set in a clear light; to exhibit distinctly or conspicuously. To prove him, and illustrate his high worth. (Milton)
3. To make clear, intelligible, or apprehensible; to elucidate, explain, or exemplify, as by means of figures, comparisons, and examples.
4. To adorn with pictures, as a book or a subject; to elucidate with pictures, as a history or a romance.
5. To give renown or honor to; to make illustrious; to glorify. Matter to me of glory, whom their hate Illustrates. (Milton)
Origin: L. Illustratus, p.p. Of illustrare to illustrate, fr. Illustris bright. See Illustrious.