c.1374, from O.Fr.
adieu, from phrase
a dieu (vous) commant "I commend (you) to God," from
a "to" (from L.
ad) +
dieu "God," from L.
deum, acc. of
deus "god," from PIE
*deiwos (see
Zeus). Originally said to the party left;
farewell was to the party setting forth.