The Collaborative International Dictionary of English v.0.48:

Souari nut \Sou*a"ri nut`\ (Bot.)
   The large edible nutlike seed of a tall tropical American
   tree (Caryocar nuciferum) of the same natural order with
   the tea plant; -- also called butternut. [Written also
   sawarra nut.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

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.
      [1913 Webster]

   2. (Bot.) The nut of the Caryocar butyrosum and Caryocar
      nuciferum, of S. America; -- called also Souari nut.
      [1913 Webster]

WordNet (r) 3.0 (2006):

butternut
    n 1: North American walnut tree having light-brown wood and
         edible nuts; source of a light-brown dye [syn: butternut,
         butternut tree, white walnut, Juglans cinerea]
    2: oily egg-shaped nut of an American tree of the walnut family