accessory vs addition

accessory

noun
  • An article that completes one's basic outfit, such as a scarf or gloves. 

  • Something that belongs to part of another main thing; something additional and subordinate, an attachment. 

  • Something in a work of art without being indispensably necessary, for example solely ornamental parts. 

  • A person who is not present at a crime, but contributes to it as an assistant or instigator. 

adj
  • Having a secondary, supplementary or subordinate function by accompanying as a subordinate; aiding in a secondary way; being additional; contributing or being contributory. Said of things and actions, very rarely of people (and then usually in a humorous version of the legal sense [or due to confusion between the noun and the adjective]). 

  • Assisting a crime without actually participating in committing the crime itself; being connected as an incident or subordinate to a principal. 

  • Present in a minor amount, and not essential. 

addition

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

  • 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. 

  • Anything that is added. 

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

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