concealment vs illustration

concealment

noun
  • The practice of keeping secrets. 

  • protection from observation or surveillance. 

  • The condition of being hidden or concealed. 

illustration

noun
  • A calculated prevision of insurance premiums and returns (life insurance) 

  • The state of being illustrated, or of being made clear and distinct. 

  • A picture designed to decorate a publication, or elucidate a literary work. 

  • The act of illustrating; the act of making clear and distinct; 

  • Something which illustrates; a comparison or example intended to make clear or apprehensible, or to remove obscurity. 

How often have the words concealment and illustration occurred in a corpus of books? (source: Google Ngram Viewer )