petro- 1
a combining form meaning "rock," "stone," used in the formation of compound words: petrology.
Also, petri-; esp. before a vowel, petr- .
[ pétra rock, pétros a stone ]
petro- 2
a combining form meaning "petroleum," "the extraction and export of petroleum," used in the formation of compound words: petrochemistry; petropower.
[ extracted from PETROLEUM ]