Coupler /(k?p"l?r)/

Coup·ler

Coupler

n.
  1. One who couples; that which couples, as a link, ring, or shackle, to connect cars.

Phrases & Compounds
Coupler of an organ
a contrivance by which any two or more of the ranks of keys, or keys and pedals, are connected so as to act together when the organ is played.