Where does “tuplaikkuna” come from?

tuplaikkuna (Finnish) comes from Finnish ikkuna, from Finnish akkuna, from Proto-Finnic *akkuna, from Old East Slavic окъно, from Proto-Slavic okъnò — window.

tuplaikkuna (Finnish): double-glazed window

Definitions

double-glazed window

Ancestry of “tuplaikkuna”, step by step

tuplaikkuna traces back through two separate lines of ancestry.

via Finnish ikkuna

Step	Language	Word	Meaning
1	Finnish	ikkuna	window; sash
2	Finnish	akkuna	Alternative form of ikkuna
3	Proto-Finnic	*akkuna	window
4	Old East Slavic	окъно	window
5	Proto-Slavic	okъnò	window

via Finnish tupla

Step	Language	Word	Meaning
1	Finnish	tupla	double
2	Swedish	dubbla	double down

Every word from Proto-Slavic okъnò →Every word from Old East Slavic окъно →Every word from Proto-Finnic *akkuna →