add-on vs subscript

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. 

subscript

noun
  • A type of lettering form written lower than the things around it. 

  • An index into an array or hash. 

verb
  • To access (an array element) by its index. 

  • To convert to a subscript form. 

  • To provide with a subscript. 

adj
  • Written underneath. 

How often have the words add-on and subscript occurred in a corpus of books? (source: Google Ngram Viewer )