noun A textured or threaded washer used to prevent components from become loose during rotation. On bicycles they are found, for example, on a bottom bracket and a track hub.
noun A ring (usually of steel) that is part of a wheelrim on some types of heavy equipment; it locks down the tire's mounting.
noun Any of various types of jewellery or components thereof, such as rings with a locking feature or rings that lock a chain closed.