Where does “wāwa” come from?

wāwa (Old English) comes from Proto-Germanic waiwô, from Proto-Indo-European wai — oh!; woe!.

Ancestry of “wāwa”, step by step

Step	Language	Word	Meaning
1	Proto-Germanic	waiwô	woe, grief, misery; evil, wickedness, malice
2	Proto-Indo-European	wai	oh!; woe!