Where does “sleep well” come from?

sleep well (English) comes from English well, from Middle English wellen, from Old English weallan, from Proto-Germanic wallaną, from Proto-Indo-European wēlH-, from Proto-Indo-European welH- — to turn, to wind.

sleep well (English): A farewell said shortly before going to bed; usually said between family members or good friends

Definitions

  1. A farewell said shortly before going to bed; usually said between family members or good friends

Ancestry of “sleep well”, step by step

sleep well traces back through two separate lines of ancestry.

via English well

StepLanguageWordMeaning
1EnglishwellAccurately, competently, satisfactorily;...
2Middle Englishwellento boil, to bubble
3Old Englishweallanto well
4Proto-Germanicwallanąto well up, spring out, bubble forth
5Proto-Indo-EuropeanwēlH-to roll, to undulate
6Proto-Indo-EuropeanwelH-to turn, to wind

via English sleep

StepLanguageWordMeaning
1EnglishsleepTo rest in a state of reduced consciousness; To...
2Middle Englishslepento sleep; to become asleep, to cause to sleep; to...
3Old Englishslǣpan
4Proto-West Germanicslāpanto sleep
5Proto-Germanicslēpanąto sleep
6Proto-Indo-Europeanslab-to be weak, be languid; be weak, limp, languid
Every word from Proto-Indo-European welH-Every word from Proto-Indo-European wēlH-Every word from Proto-Germanic wallaną