Relay

1) an electrical device in which a small change in current or voltage controls the switching on or off of circuits or other devices.
2) an electromagnetic or electronic switching device activated by a signal and usually used to control a large current or to activate another device or circuit.
an electromagnetic device for remote or automatic control that is actuated by variation in conditions of an electric circuit and that operates in turn other devices (such as switches) in the same or a different circuit.

Sources:

Англійський словник Коллінза, електронний ресурс: https://www.collinsdictionary.com/

Словник Webster's Dictionary https://www.merriam-webster.com/