1. An acknowledgment or expression of goodwill at parting; SYN. word of farewell.
2. The act of departing politely; SYN. leave, leave-taking, parting.

ETYM Old Eng. val, French val, Latin vallis. Related to Avalanche, Vail to lower, Valley.
(Homonym: veil) (Latin) “farewell”.
A tract of low ground, or of land between hills; a valley.

S.Germany
An expression uttered when on leaves.