Merriam-Webster's Collegiate® Dictionary, 11th Edition
ACCESSORY
I. noun also accessary (plural -ries)
Date: 15th century
1. a person not actually or constructively present but contributing as an assistant or instigator to the commission of an offense, a person who knowing that a crime has been committed aids or shelters the offender with intent to defeat justice,
2. a thing of secondary or subordinate importance ; adjunct , an object or device not essential in itself but adding to the beauty, convenience, or effectiveness of something else ,
II. adjective
Date: 1607
assisting as a subordinate, aiding or contributing in a secondary way ; supplementary , present in a minor amount and not essential as a constituent