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From The Collaborative International Dictionary of English v.0.48:
Petroleum \Pe*tro"le*um\ (p[-e]*tr[=o]"l[-e]*[u^]m), n. [NL., fr. L. petra a rock + oleum oil: cf. F. p['e]trole. Cf. Petrify, and Oil.] Rock oil, mineral oil, or natural oil, a dark brown or greenish inflammable liquid, which, at certain points, exists in the upper strata of the earth, from whence it is pumped, or forced by pressure of the gas attending it. It consists of a complex mixture of various hydrocarbons, largely of the methane series, but may vary much in appearance, composition, and properties. It is refined by distillation, and the products include kerosene, benzine, gasoline, paraffin, etc. [1913 Webster] Petroleum spirit, a volatile liquid obtained in the distillation of crude petroleum at a temperature of 170[deg] Fahr., or below. The term is rather loosely applied to a considerable range of products, including benzine and ligroin. The terms petroleum ether, and naphtha, are sometimes applied to the still more volatile products, including rhigolene, gasoline, cymogene, etc. [1913 Webster] Petroleur