Accessory is a noun or adjective, meaning “a helper” or “a non-essential object, something secondary.” It is most often spelled accessory, with an “o;” however, accessary (with an “a”) is also considered acceptable as a noun—but not as an adjective:
Accessory (noun): He was accused of being an accessory to the crime because he drove the getaway car.
Accessary (noun),less common: Her new computer came with several accessaries— a webcam, extra mouse, and dust-shield.
Accessory (adjective): She played an accessory role in the crime, on the lookout for police.
Because accessary, with an “a,” is becoming less common now, some people may consider it completely unacceptable. You can play it safe by using only accessory.