Where does “*akkuna” come from?

*akkuna (Proto-Finnic) comes from Old East Slavic окъно, from Proto-Slavic okъnò.

Ancestry of “*akkuna”, step by step

Step	Language	Word	Meaning
1	Old East Slavic	окъно	window
2	Proto-Slavic	okъnò	—

*akkuna — Etymology, Origin & Word History | Etymology Explorer