coupler

noun5

1. •
   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. — 1954
2. •
   A device that connects two keyboards of an organ together so that they play together.
3. •
   An electrical device used to transfer energy from one electric device to another, especially without a physical connection.
4. •
   A device used to convert electronic information into audible sound signals for transmission over telephone lines.
5. •
   (no longer used) Someone who couples things together, especially someone whose job it is to couple railway carriages.