Noun

• S: (n) accessory, accoutrement, accouterment (clothing that is worn or carried, but not part of your main clothing)
• S: (n) accessory, appurtenance, supplement, add-on (a supplementary component that improves capability)
• S: (n) accessory, accessary (someone who helps another person commit a crime)

Adjective

• S: (adj) accessary, accessory (aiding and abetting in a crime) "he was charged with being accessory to the crime"
• S: (adj) accessory, adjunct, ancillary, adjuvant, appurtenant, auxiliary (furnishing added support) "an ancillary pump"; "an adjuvant discipline to forms of mysticism"; "The mind and emotions are auxiliary to each other"