Source : Webster's Revised Unabridged Dictionary (1913)

   Note: In some parts of America, especially in New England,
         the name walnut is given to several species of hickory
         ({Carya}), and their fruit.

   {Ash-leaved walnut}, a tree ({Juglans fraxinifolia}), native
      in Transcaucasia.

   {Black walnut}, a North American tree ({J. nigra}) valuable
      for its purplish brown wood, which is extensively used in
      cabinetwork and for gunstocks. The nuts are thick-shelled,
      and nearly globular.

   {English}, or {European}, {walnut}, a tree ({J. regia}),
      native of Asia from the Caucasus to Japan, valuable for
      its timber and for its excellent nuts, which are also
      called Madeira nuts.

   {Walnut brown}, a deep warm brown color, like that of the
      heartwood of the black walnut.

   {Walnut oil}, oil extracted from walnut meats. It is used in
      cooking, making soap, etc.

   {White walnut}, a North American tree ({J. cinerea}), bearing
      long, oval, thick-shelled, oily nuts, commonly called
      butternuts. See {Butternut}.

Source : WordNet®

walnut oil
     n : oil from walnuts