coupler

noun

1. (archaic)Someone who couples things together, especially someone whose job it is to couple railway carriages.
2. Anything that serves to couple things together; but especially a device that couples railway carriages.

   “Another example of up-to-date practice is that all locomotives and rolling stock have automatic couplers.”

3. A device that connects two keyboards of an organ together so that they play together.
4. A device used to convert electronic information into audible sound signals for transmission over telephone lines.
5. An electrical device used to transfer energy from one electric device to another, especially without a physical connection.