'adieu' originates from Old French, specifically the phrase 'a Dieu', where 'a' meant 'to' and 'Dieu' meant 'God'.

'a Dieu' transformed into the French word 'adieu', and eventually became the modern English word 'adieu' through Middle English.

Initially, it meant 'to God', but over time it evolved into its current meaning of 'farewell'.