Is the tomato a fruit or a vegetable? The confusion arises because of the differences in usage between scientists and cooks. Scientifically speaking, a tomato is definitely a fruit. True fruits are developed from the ovary in the base of the flower, and contain the seeds of the plant. As far as cooking is concerned, some things which are strictly fruits, such as tomatoes or bean pods, may be called ‘vegetables’ because they are used in savoury rather than sweet cooking.
The fruit vs vegetable debate had legal implications in the United States. In 1887, U.S. tariff laws that imposed a duty on vegetables, but not on fruits, caused the tomato’s status to become a matter of legal importance. In Nix v. Hedden, the U.S. Supreme Court settled the controversy in 1893 by deciding that the tomato is a vegetable, based on the popular definition that classifies vegetables by use, that they are generally served with dinner and not dessert. This decision applied only to the interpretation of the Tariff Act of March 3, 1883, and the court did not purport to reclassify the tomato for botanical or other purposes.
Nix v. Hedden has been cited in three Supreme Court decisions as a precedent for court interpretation of common meanings, especially dictionary definitions. In 2005, supporters in the New Jersey legislature cited the case as a basis for a bill designating the tomato as the official state vegetable. (Oxford Dictionaries, Wikipedia)