Illustrate, v. t. [imp. & p. p. Illustrated; p. pr. & vb. n. Illustrating.]
Etymology: [L. illustratus, p.p. of illustrare to illustrate, fr. illustris bright. See Illustrious.]
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. Shak. 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.
1 more senses
5. To give renown or honor to; to make illustrious; to glorify. [Obs.] Matter to me of glory, whom their hate Illustrates. Milton.
1 other Webster entry under this spelling
Illustrate, a.
Illustrated; distinguished; illustrious. [Obs.] This most gallant, illustrate, and learned gentleman. Shak.
Shades of meaning
Fernald has no entry of its own for illustrate; he lists it under adorn.
Where he writes about it:
To embellish is to brighten and enliven by adding something that is not necessarily or very closely connected with that to which it is added; to illustrate is to add something so far like in kind as to cast a side-light upon the principal matter. — from adorn