From The Food Encyclopedia by Jacques Rolland and Carol Sherman
Also oilnut, white walnut. The edible nut of the native North American white walnut tree, Juglans cinerea, with a dark brown, deeply grooved shell and rich oily meat, grown from southern Quebec to Georgia and from eastern Minnesota to the eastern coast of the United States. Native Americans pressed butternuts for their rich oil, which was used ceremonially and for cooking. Because of their high oil content, the nuts go rancid quickly and must be used soon after they are harvested.
