n.
Pronunciation: p ə - ' tr ō -l ē - ə m, - ' tr ō l-y ə m
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