Adieu and Bye bye

Adieu noun - An expression of good wishes at parting.

Bye bye and adieu are semantically related In some cases you can use "Bye bye" instead the word "Adieu" as a noun or a interjection.

Adieu and bye bye are semantically related in departure topic. You can use "Adieu" instead the phrase "Bye bye" as a noun or a interjection, if it concerns topics such as goodbye, farewell statement, have a nice trip.