A contraction of the phrase God be with you (or ye); see GOD¹ (below). The substitution of good- for God may have been due to association with such formulas of leave-taking as good day, good night, etc.
It has been suggested that the phrase may have originated in God buy you = ‘God redeem you’, and that association with God be with you is of later date. This is not supported by the earliest forms, which as a rule show that the expression was known to be a clipped one.
Alternate: A colloquial and nursery variant is Bye Bye that is a sound used to lull a child to sleep; hence, a childish name for ‘sleep’ or ‘bed’.
1. GOD - In phrases expressive of a strong wish, chiefly for the benefit or injury of some person, as God bless, damn, help, preserve, save, shield, speed, yield (you, him, etc.); also God forbid, grant (that); God give (something): for these see the various verbs. Hence occasionally used in participial expressions.
Some of these phrases assumed abbreviated or corrupted forms through frequent use, as God eyld (ild, dild) you, goddilge yee = God yield you; God b'wy (buy) ye = God be with you; God (Godge) you good even = God give you, etc. (also God dig-you-den, God(g)igoden. In such phrases as have remained current, God is often omitted, as bless you, damn you, preserve us.
- 1. As an exclamation: A form of address at parting; farewell. Also in to bid, say good bye (to).
- b. abbreviated; cf. BYE-BYE.
- 2. n. A saying ‘good-bye’; a parting greeting. Hence goodbyer, one who says ‘good-bye’; goodbying vbl. n., saying ‘good-bye’.