Where does “Satu” come from?

Satu (Finnish) comes from Finnish satu, from Finnish sattua, from Proto-Finnic sattudak.

Ancestry of “Satu”, step by step

Step	Language	Word	Meaning
1	Finnish	satu	fairy tale; fable; tale
2	Finnish	sattua	to hurt , be sore; to happen, to be , occur, come...
3	Proto-Finnic	sattudak	—