farewell (interj.)

expression at parting, late 14c., from Middle English faren wel, verbal phrase attested by c. 1200 (see fare (v.) + well (adv.)); usually said to the departing person, who replied with good-bye. As a noun, "a good-bye, a leave-taking," by early 15c. Expression to a fare-thee-well "to the last degree" is by 1884, American English.

Others are reading

Definitions of farewell from WordNet

farewell (n.)
an acknowledgment or expression of goodwill at parting;
Synonyms: word of farewell
farewell (n.)
the act of departing politely;
he disliked long farewells
Synonyms: leave / leave-taking / parting