tung oil, oil obtained from the seeds of a tropical tree, the tung tree ( Aleurites fordii ) of the spurge family, and from seeds of some related species, all from Indomalesia or W Pacifica. It is known also as China wood oil and nut oil. The poisonous seeds found in the heart of the tung fruit (which is the size of a small apple) contain more than 50% tung oil, readily obtained when the seeds are heated, ground, and pressed. The oil is amber-colored and contains a high proportion of eleostearic acid. Because of its wide use as a dryer in varnishes and paints, it has great commercial importance. While the bulk of the product is utilized by the paint and varnish industry, tung oil has additional uses, e.g., as a component of insulating compounds and in the manufacture of linoleum and oilcloth. China was long the chief producer of the oil, but the tree has been introduced in other areas as well. The U.S. Dept. of Agriculture experimented with tung tree growing early in the 20th cent., and afterward encouraged Southern farmers to cultivate it. In recent years, an increasing portion of the commercial supply has been obtained from trees grown in the United States, particularly in the South.