Accessory

Accompanying as a subordinate; aiding in a secondary way; additional; connected as an incident or subordinate to a principal; contributing or contributory; said of persons and things, and, when of persons, usually in a bad sense; as, he was accessory to the riot; accessory sounds in music.

That which belongs to something else deemed the principal; something additional and subordinate.

Same as Accessary, n.

Anything that enters into a work of art without being indispensably necessary, as mere ornamental parts.

someone who helps another person commit a crime

furnishing added support; "an ancillary pump"; "an adjuvant discipline to forms of mysticism"; "The mind and emotions are auxiliary to each other"

aiding and abetting in a crime; "he was charged with being accessory to the crime"