Where does “Hallows' Eve” come from?

Hallows' Eve (English) comes from English all, from Middle English all, from Old English eall, from Proto-West Germanic all, from Proto-Germanic allaz, from Proto-Indo-European h₂él- — to grow, nourish.

Ancestry of “Hallows' Eve”, step by step

Hallows' Eve traces back through 3 separate lines of ancestry.

via English all

StepLanguageWordMeaning
1EnglishallEvery individual or anything of the given class,...
2Middle Englishallall; all, every
3Old Englisheallall; whole, entire; everything
4Proto-West Germanicallall
5Proto-Germanicallazall
6Proto-Indo-Europeanh₂él-to grow, nourish

via English hallow

StepLanguageWordMeaning
1EnglishhallowA saint; a holy person; an apostle; The relics or...
2Middle Englishhalwesaint; The shrine of a saint
3Old Englishhālgaa holy one, saint; holy man, saint
4Proto-Germanichailagôholy one
5Proto-Germanichailazwhole, unbroken, intact; entire, complete; hale,...
6Proto-Indo-European*kéh₂iloshealthy

via English Eʋe

StepLanguageWordMeaning
1EnglishEʋe
2Middle EnglishEve
3Old FrencheveAlternative form of iaue; water
4Latinaquawater
5Proto-Italicakʷāwater
6Proto-Indo-Europeanh₂ekʷeh₂water, flowing water
Every word from Proto-Indo-European h₂él-