'deoil' originates from Latin prefix 'de-' and Old French/Old English word 'oil' (Old French 'oile', from Latin 'oleum'), where 'de-' meant 'off, away' and 'oleum' meant 'oil'.

'deoil' is a modern technical formation (written as 'de-oil' in some sources) created by attaching the Latin-derived prefix 'de-' to the noun 'oil' (from Old French 'oile' < Latin 'oleum'), forming a verb meaning 'remove oil'.

Initially formed to mean 'remove oil' in technical/industrial contexts, and this core meaning has been retained in modern usage (mainly in industrial, cleaning, and processing vocabulary).