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

plural of coupler

plural of acoustic 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 Janney 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.