valediction (n.) Look up valediction at Dictionary.com
"a farewell, a bidding farewell," 1610s, from past participle stem of Latin valedicere "bid farewell, take leave," from vale "farewell!," second person singular imperative of valere "be well, be strong" (from PIE root *wal- "to be strong") + dicere "to say" (from PIE root *deik- "to show," also "pronounce solemnly").