noun / interjection
adieu
uh-DOO/əˈduː/
A goodbye.
The departing guest bids his host adieu with a small bow.

Etymology
Literally “to God,” adieu shortened expressions such as “I commend you to God.” A blessing for someone being left became a general farewell.
In context
Fare thee well at once! The glow-worm shows the matin to be near, And 'gins to pale his uneffectual fire: Adieu, adieu!