add-on vs addition

add-on

noun
  • Something which can be appended to something else. 

  • A software extension or hardware peripheral that provides additional functions or customization for a core application or system. 

  • Additional chips that can be purchased at specific times in tournament play. 

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 add-on and addition occurred in a corpus of books? (source: Google Ngram Viewer )