opium

English opium was borrowed from Latin opium, which came from Ancient Greek ὄπιον (ópion), a diminutive form built on ὀπός (opós), meaning 'juice of a plant.' That root goes back to Proto-Indo-European *sokʷós, meaning 'juice, resin.'

The word narrowed as it traveled: from a general Greek term for plant juice, to a small, specific noun for the poppy's exudate, to the fixed Latin and English name for that one substance.

The Greek diminutive ending seen in ópion (-ĭον) marks it as literally a 'little juice.'