appendix vs explanation

appendix

noun
  • A text added to the end of a book or an article, containing additional information. 

  • Any process, prolongation, or projection. 

  • The vermiform appendix. 

explanation

noun
  • Something that explains, makes understandable. 

  • A resolution of disputed points pursuant to discussion; a mutual clarification of disputed points; reconciliation. 

  • The act or process of explaining. 

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