1 [C] a drawing or picture in a book, magazine, etc. especially one that explains sth:
50 full-colour illustrations
2 [U] the process of illustrating sth:
the art of book illustration
3 [C,U] a story, an event or an example that clearly shows the truth about sth:
The statistics are a clear illustration of the point I am trying to make * Let me, by way of illustration, quote from one of her poems.
