Where does “okénce” come from?

okénce (Old Czech) comes from Old Czech -cě, from Proto-Slavic -ьca, from Proto-Slavic -ьka, from Proto-Balto-Slavic -ikaʔ, from Proto-Indo-European -ikeh₂.

Ancestry of “okénce”, step by step

Step	Language	Word	Meaning
1	Old Czech	-cě	—
2	Proto-Slavic	-ьca	Denominal, forms diminutives; Deverbal , forms...
3	Proto-Slavic	-ьka	—
4	Proto-Balto-Slavic	-ikaʔ	—
5	Proto-Indo-European	-ikeh₂	—

Every word from Proto-Indo-European -ikeh₂ →Every word from Proto-Slavic -ьka →Every word from Old Czech -cě →