Where does “heiligen” come from?

heiligen (Middle Dutch) comes from Old Dutch hēlagon, from Proto-Germanic hailagaz, from Proto-Germanic hailaz, from Proto-Indo-European *kéh₂ilos.

Ancestry of “heiligen”, step by step

Step	Language	Word	Meaning
1	Old Dutch	hēlagon	—
2	Proto-Germanic	hailagaz	holy, sacred
3	Proto-Germanic	hailaz	whole, unbroken, intact; entire, complete; hale,...
4	Proto-Indo-European	*kéh₂ilos	—

heiligen — Etymology, Origin & Word History | Etymology Explorer