Definition of "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.  examples

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

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

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