Main Entry: pe·tro·leum

Pronunciation: \pə-ˈtrō-lē-əm, -ˈtrōl-yəm\

Function: noun

Etymology: Middle English, from Medieval Latin, from Latin petr- + oleum oil — more at oil

Date: 15th century

: an oily flammable bituminous liquid that may vary from almost colorless to black, occurs in many places in the upper strata of the earth, is a complex mixture of hydrocarbons with small amounts of other substances, and is prepared for use as gasoline, naphtha, or other products by various refining processes