Real Dictionary

accessory
a supplementary part or object, as of a car, appliance, etc [...]
Accessories are articles such as belts and scarves which you wear or carry but which are not part of your main clothing.
Accessories are items of equipment that are not usually essential, but which can be used with or added to something else in order to make it more efficient, useful, or decorative.
any of a large group of nitrogenous compounds of high molecular weight that are essential constituents of all living organisms. They consist of one or more chains of amino acids linked by peptide bonds and are folded into a specific three-dimensional shap
You can use accessory to describe something which is part of an activity or process, but not the most essential or important part of it.
countable noun: If someone is guilty of being an accessory to a crime, they helped the person who committed it, or knew it was being committed but did not tell the police.