I. |pe.trō+ adjective
Etymology: petr- + chemical, adjective
1. : of or relating to the chemistry of rocks
a thorough petrochemical study of certain weathering profiles — F.J.Pettijohn
2.
a. : of or relating to the production of petrochemicals
the petrochemical industry
b. : produced as a petrochemical
petrochemical acetone
II. noun
Etymology: petr- + chemical, n.
: a chemical isolated from petroleum or natural gas or a derivative produced from such a substance by chemical reaction — used chiefly commercially
chemicals derived from petroleum and natural gas, such as ammonia, carbon black, and thousands of organic chemicals, are classified as petrochemicals — Chemical & Engineering News