remontoire
small secondary source of power, a weight or spring, which runs a timekeeping mechanism and is itself periodically rewound by the timepiece's main power source, such as a mainspring
en-US/ˌɹɛmənˈtwɑɹ/
small secondary source of power, a weight or spring, which runs a timekeeping mechanism and is itself periodically rewound by the timepiece's main power source, such as a mainspring