From Greek 'elaion' (olive oil), via Latin 'oleum' — all oil was originally olive oil; the word expanded as new oils were discovered.
A viscous liquid derived from petroleum, plants, or animals.
From Old French 'oile,' from Latin 'oleum' meaning 'oil, olive oil,' from Greek 'elaion' (olive oil), from 'elaia' (olive tree). Oil was originally and specifically olive oil. Key roots: elaia (Greek: "olive, olive tree").