oil: [12] Around the Mediterranean in ancient times the only sort of oil encountered was that produced by pressing olives, and so ‘oil’ was named after the olive. The Greek word for ‘olive’ was elaíā, and from it was derived elaíon ‘olive oil’. This passed into Latin as oleum, and reached English via Old French oile. By now it had begun to be applied to similar substances pressed from nuts, seeds, etc, but its specific modern use for the mineral oil ‘petroleum’ is a much more recent, essentially 19th-century development. => olive[oil etymology, oil origin, 英语词源]