The story
- Proto-Indo-European*ǵʰew-
- Proto-Indo-European*ǵʰutós?
- Proto-Germanic*gudą
- Proto-West Germanic*god
- Old Englishgod
- Middle Englishgod
- Middle EnglishGod
- EnglishGod
- Proto-Indo-European*bʰuH-
- Proto-Indo-European*bʰuHyétider.?
- Proto-Germanic*beuną
- Proto-West Germanic*beun
- Old Englishbēon
- Middle Englishbeen
- Englishbe
- Proto-Indo-European*dwóh₁
- Proto-Indo-European*dwi-
- Proto-Indo-European*wí
- Proto-Indo-European*wíteros
- Proto-Indo-European*wíterom
- Proto-Germanic*wiþrą
- Proto-West Germanic*wiþr
- Old Englishwiþerclip.
- Old Englishwiþ
- Middle Englishwiþ
- Englishwith
- Proto-Indo-European*yúHs
- Proto-Indo-European*uswé
- Proto-Indo-European*uswís
- Proto-Germanic*izwiz
- Proto-West Germanic*iwwiz
- Old Englishēow
- Middle Englishyow
- Englishyou
- Englishgoodinflu.
- English todaygoodbye
From earlier goodby, Godby, Godby'e, Godbwye, God b'w'y, God bwy yee, God buy you, God be wi' you, each a progressively shorter contraction of God be with ye or God be with you. Note the change of God to good by confusion with good morning, good night, etc. Modernly analysed as good + bye.
Etymology from Wiktionary, CC BY-SA 4.0.