American Dictionary of the English Language

BUT'TERNUT, noun [butter and nut.]

The fruit of an American tree, the Juglans cinerea; so called from the oil it contains. The tree bears a resemblance, in its general appearance, to the walnut, or black walnut, so called. It is sometimes called oilnut and white walnut. The tree is called also butternut or butternut-tree. Dr. M. Cutler calls it Juglans Cathartica.