The Collaborative International Dictionary of English v.0.48:

Downcome \Down"come`\ (doun"k[u^]m`), n.
   1. Sudden fall; downfall; overthrow. --Milton.
      [1913 Webster]

   2. (Iron Manuf.) A pipe for leading combustible gases
      downward from the top of the blast furnace to the
      hot-blast stoves, boilers, etc., where they are burned.
      [1913 Webster]