Source : Webster's Revised Unabridged Dictionary (1913)

Coupler \Coup"ler\ (k?p"l?r), n.
   One who couples; that which couples, as a link, ring, or
   shackle, to connect cars.

   {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.