Source : Webster's Revised Unabridged Dictionary (1913)

Petroleum \Pe*tro"le*um\, 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.

   {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.

Source : WordNet®

petroleum
     n : a dark oil consisting mainly of hydrocarbons [syn: {crude
         oil}, {crude}, {rock oil}, {fossil oil}]