coupler

(now rare) Someone who couples things together, especially someone whose job it is to couple railway carriages.

Anything that serves to couple things together; but especially a device that couples railway carriages.

(music) A device that connects two keyboards of an organ together so that they play together.

A device used to convert electronic information into audible sound signals for transmission over telephone lines.

An electrical device used to transfer energy from one electric device to another, especially without a physical connection.