One of the mysteries of the English language finally explained.
A tropical American shrub, Jatropha curcas (family Euphorbiaceae), having large, roundish to heart-shaped, sometimes lobate leaves and a reddish, milky sap (more fully "physic-nut bush", "physic-nut tree"); the fruit or seed of this shrub, yielding pulza oil and used as a purgative. Also: any of various other tropical American plants, especially of the genus Jatropha, whose seeds have a similar purgative effect, especially (a) (more fully "French physic nut") J. multifida; (b) (more fully "wild physic nut") J. gossypiifolia.
Mid 17th century; earliest use found in Richard Ligon (c1585–1662), business agent and natural science writer. From physic + nut.
physic nut/ˈfɪzɪk ˌnʌt/
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