accessary vs add-on

accessary

noun
  • Someone who accedes to some act, now especially a crime; one who contributes as an assistant or instigator to the commission of an offense. 

adj
  • Accompanying as a subordinate; additional; accessory; especially, uniting in, or contributing to, a crime, but not as chief actor. See accessory. 

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. 

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