An accessory is a thing that is used to support or enhance an activity, but which is not essential to it. In other words, it's something additional that can be helpful, but isn't required for the basic functioning of whatever it is you're doing.
Usage examples
An accessory to complete a formal outfit for men could be a tie or a pocket square.
A handbag or clutch can be considered as an essential accessory for many women.
If you're looking for accessories for the new Moto Z, we're here to help you find the best ones out there. (androidcentral.com)
It could work with flats or heels, and can take a wide array of accessories with all the color options. (fashables.com)
Play it safe by painting it white and work colour in with accessories for a look that can be changed year - on - year with minimal fuss. (idealhome.co.uk)