Where does “-iain” come from?

-iain (Ingrian) comes from Ingrian -in, from Proto-Finno-Ugric *-in, from Proto-Uralic -ma.

Ancestry of “-iain”, step by step

Step	Language	Word	Meaning
1	Ingrian	-in	—
2	Proto-Finno-Ugric	*-in	—
3	Proto-Uralic	-ma	—

-iain — Etymology, Origin & Word History | Etymology Explorer