Adieu, interj. & adv.
Etymology: [OE. also adew, adewe, adue, F. dieu, fr. L. ad to + deus God.]
Good-by; farewell; an expression of kind wishes at parting.
1 other Webster entry under this spelling
Adieu, n.; pl. Adieus.
A farewell; commendation to the care of God at parting. Shak.
Shades of meaning
Fernald has no entry of its own for adieu; he lists it under farewell.
Where he writes about it:
Adieu, from the French, is still more ceremonious than farewell; conge, also from the French, is commonly contemptuous or supercilious, and equivalent to dismissal. — from farewell
Antonyms
none given