accessory; appurtenance
Legal term for a thing that is attached to and serves a principal thing, such as a key to a lock or a remote control to a TV. Not used for fashion accessories.
Under the Civil Code, an accessory is deemed to follow the disposition of the principal thing.
The house key is regarded as an accessory to the building.
Compound of 従 (follow, subordinate) and 物 (thing), directly reflecting the legal concept of a subordinate thing.