Source : Webster's Revised Unabridged Dictionary (1913)

Butternut \But"ter*nut`\, n.
   1. (Bot.) An American tree ({Juglans cinerea}) of the Walnut
      family, and its edible fruit; -- so called from the oil
      contained in the latter. Sometimes called {oil nut} and
      {white walnut}.

   2. (Bot.) The nut of the {Caryocar butyrosum} and {C.
      nuciferum}, of S. America; -- called also {Souari nut}.