D defs.my
Entry 1 sense Webster, 1913

Coupler

/(k?p"l?r)/ · Coup·ler · IPA /ˈkʌp(ə)lə/
01 n. One who couples; that which couples, as a link, ring, or shackle, to connect cars.
  1. 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.