accessory

Short definition from Wiktionary

Adjective

1. 1
   Having a secondary, supplementary or subordinate function by accompanying as a subordinate; aiding in a secondary way; being additional; contributing or being contributory.
2. 2
   Assisting a crime without actually participating in committing the crime itself; being connected as an incident or subordinate to a principal.
3. 3
   Present in a minor amount, and not essential.

Noun

1. 1
   Something that belongs to part of another main thing; something additional and subordinate, an attachment.
2. 2
   An article that completes one's basic outfit, such as a scarf or gloves.
3. 3
   A person who is not present at a crime, but contributes to it as an assistant or instigator.
4. 4
   Something in a work of art without being indispensably necessary, for example solely ornamental parts.