†4.pseudo-archaic. With omission of give, in Gad ye good night: ‘goodnight’; = God you good night at godn. and int. Phrases 1c(b)(i). Obsolete. rare.
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the world > action or operation > behaviour > good behaviour > courtesy > courteous act or expression > courteous formulae [phrase] > expressions of leave-taking > at night
goodnightc1275
Gad ye good night1849
(good night) sleep tight1933
1849 G. P. R. JamesWoodman I. xv. 327Gad ye good night, lords and ladies.