Adieu is a farewell, in a formal or literary way. Bid adieu, a last adieu, adieu to all that.
It is French and English at once: kept in English for weight, and used for a parting that is final rather than a see you tomorrow. Bid adieu is the standard phrase. The French means to God, short for I commend you to God.
1nounadieuA farewell, in a formal or literary way.
“With a last wave from the deck of the ship, she bade adieu to her homeland.”
adieu is a farewell.
Old French adieu shortens a Dieu vous comant, I commend you to God, from Latin deus, a god.
Medieval Latin
ad Deum — to God
Old French
adieu — to God
Middle English
adieu
English, today
adieu
Built from
From Middle English adieu also adew, adewe, adue, from Old French adieu (“to God”), a shortening of a Dieu vous comant (“I commend you to God”), from Medieval Latin ad Deum (“to God”). a doublet of adios.
Etymology from Wiktionary, CC BY-SA