Common Mistake In English description

Accessary is a noun, usually used in British criminal law, which describes someone who helps another person commit a crime.

For example: "He was charged as an accessary to murder.."

Accessory is a noun, used to describe something that can be added to a machine or to clothing, which has a useful or decorative purpose.

For example: "An old outfit can be revamped with a simple new accessory."

!Note - In the USA, accessory is the spelling for both senses.