noun

A thing which can be added to something else in order to make it more useful, versatile, or attractive.

optional accessories include a battery charger and shoulder strap

attachment,extra,addition,add-on,retrofit,adjunct,appendage,appurtenance,component,additional component,fitment,supplement

adjective

Contributing to or aiding an activity or process in a minor way; subsidiary or supplementary.

functionally the maxillae are a pair of accessory jaws

additional,extra,supplementary,supplemental,auxiliary,ancillary,secondary,subsidiary,supportive,assisting,reserve,complementary,further,more,add-on