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

plural of coupler

An interface device for coupling electrical signals by acoustical means. / (dated, telecommunications) A terminal device used to link data terminals and radio sets with the telephone network.

plural of acoustic coupler

A semi-automatic form of railway coupling allowing cars and locomotives to be securely linked together without rail workers having to get between the vehicles.

plural of Janney coupler