köken: Borrowed from Medieval Latin ad Deum (“to God”). Compare Aragonese, Asturian, Extremaduran, and Spanish adiós, Catalan adeu, Dutch ajuus, English, French, and Occitan adieu, German tschüss, Greek αντίο (antío), Galician adeus, Italian addio, Maltese addiju, Mirandese adius, Romanian adio, Serbo-Croatian ади̏о/adȉo, Slovene adȋjo.
a final expression of departure: farewell, so long, adieu, goodbye · a non-final expression of departure: goodbye, au revoir
eş: さよなら, 失礼します, それでは, では, バイバイ, じゃあ
köken: Shortening of earlier 左(さ)様(よう)ならば (sayō naraba), itself a compound of 左(さ)様(よう) (sayō, “like that, that way”) + ならば (naraba, “if”, now somewhat archaic, often replaced by なら (nara)). Literally, “if that's the way it is”. First cited to roughly 1742 as a conjunction (Literally, “if it's like that, then...”). The interjection usage is cited to 1788, and then the noun sense is cited to roughly 1915.
köken: Borrowed from Classical Persian اَلوِدَاع (alwidā'), an unadapted borrowing from Arabic الوَدَاع (al-wadāʕ), whence also विदा (vidā, “departure”). Cognate with Turkish elveda.
hi (greeting) · hey (to get someone's attention) · bye (often repeated twice: hei hei)
köken: From Proto-Finnic *hei (compare Estonian hei, Ingrian hei, Karelian hei, Ludian hei, Veps hei). Compare also Old Norse hei (whence Swedish hej) and English hey.
köken: Borrowed from Italian ciao (“hi”), from Venetan s-ciao, sciavo (“slave”) (in particular the expression s-ciao vostro, literally meaning "(I am) your slave" but in essence meaning "your humble servant"), from Medieval Latin sclavus (“slave”). Doublet of szláv. See also the similar etymology at szervusz and alászolgája.
köken: Non-Sino-Vietnamese reading of Chinese 朝 (“to meet; to meet a senior person; to attend the emperor's audience”, SV: triều). Doublet of chầu and triều. (Nguyễn Văn Khang. Từ ngoại lai trong tiếng Việt, 2007) False cognate of Italian ciao, which also means both "hello" and "goodbye".