addendum vs addition

addendum

noun
  • Something to be added; especially text added as an appendix or supplement to a document. 

  • The height by which the tooth of a gear projects beyond (outside for external, or inside for internal) the standard pitch circle or pitch line. 

  • A postscript. 

addition

noun
  • Anything that is added. 

  • The act of adding anything. 

  • The arithmetic operation of adding. 

  • A dot at the right side of a note as an indication that its sound is to be lengthened one half. 

  • A title annexed to a person's name to identify him or her more precisely. 

  • Something added to a coat of arms, as a mark of honour. 

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