Nouns

(n)accessory, accoutrement, accoutermentclothing that is worn or carried, but not part of your main clothing
(n)accessory, appurtenance, supplement, add-ona supplementary component that improves capability
(n)accessory, accessarysomeone who helps another person commit a crime

Adjectives

(s)accessary, accessoryaiding and abetting in a crime“he was charged with being accessory to the crime”
(s)accessory, adjunct, ancillary, adjuvant, appurtenant, auxiliaryfurnishing added support“an ancillary pump”, “an adjuvant discipline to forms of mysticism”, “The mind and emotions are auxiliary to each other”