illustrate vs mean to say

illustrate

verb
  • To clarify something by giving, or serving as, an example or a comparison. 

  • To provide a book or other publication with pictures, diagrams or other explanatory or decorative features. 

mean to say

verb
  • To imply or intend to convey with one's words; used to correct or clarify one's previous utterance, or to seek such clarification. 

How often have the words illustrate and mean to say occurred in a corpus of books? (source: Google Ngram Viewer )