1.adjectiveHaving a secondary, supplementary or subordinate function by accompanying as a subordinate; aiding in a secondary way; being additional; being connected as an incident or subordinate to a principal; contributing or being contributory. Said of people and things, and, when of people, usually in a bad sense
"She was accessory to the riot."
2.adjectiveAssisting a crime without actually participating in committing the crime itself.
3.adjectivePresent in a minor amount, and not essential.