'petrochemical' originates from the combining form 'petro-' (from Greek) and the word 'chemical' (from Greek/Latin through Medieval usage), where 'petro-' ultimately came via 'petroleum' and 'petra' meant 'rock' and 'chemical' derived from Greek 'khēmia' meaning the art of transmutation.

'petrochemical' was formed in English in the 20th century by combining 'petro-' (from 'petroleum') with 'chemical'; the term arose as large-scale refining and chemical processing of petroleum and natural gas created a distinct class of industrial chemicals.

Initially it referred specifically to chemicals derived from petroleum; over time the meaning has remained largely the same and now commonly covers chemicals derived from both petroleum and natural gas.