Source : Webster's Revised Unabridged Dictionary (1913)

Valediction \Val`e*dic"tion\, n. [L., valedicere, valedictum, to
   say farewell; vale farewell (imperative of valere to be
   strong or well) + dicere to say. See {Valiant}, {Diction}.]
   A farewell; a bidding farewell. --Donne.

Source : WordNet®

valediction
     n 1: a farewell oration delivered by the most outstanding member
          of a graduating class [syn: {valedictory address}, {valedictory}]
     2: the act of saying farewell