Definition of "adieu"

adieu

/əˈdju/

interjection
1. Said to wish a final farewell; goodbye.
  Quotations
  BEATRICE. What fire is in mine ears? Can this be true?Stand I condemn'd for pride and scorn so much?Contempt, farewell! and maiden pride, adieu!No glory lives behind the back of such.
  1598–1599 (first performance), William Shakespeare, “Much Adoe about Nothing”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act III, scene i]
noun
plural adieux or adieus
1. A farewell, a goodbye; especially a fond farewell, or a lasting or permanent farewell.
  Quotations
  As Noyes bade me adieu and rode off northward in his car I began to walk slowly toward the house.
  1931, H. P. Lovecraft, chapter 6, in The Whisperer in Darkness
  At the of his so remote, so near, 1884 summer Van, before leaving Ardis, was to make a visit of adieu to Ada's larvarium.
  1969, Vladimir Nabokov, Ada or Ardor: A Family Chronicle