the.com/adieu

means A farewell — formal, old-fashioned, and a little theatrical — used when 'bye' feels too small for the moment.

from Borrowed whole from French, where 'à Dieu' means 'to God,' short for something like 'I commend you to God' — a farewell that doubled as a blessing. English absorbed it in the medieval period, kept the spelling, and over time gave it a slightly stagy, affected flavor it never had in French, where it's just an ordinary (and rather final) way to say goodbye.