Where does “siistiys” come from?

siistiys (Finnish) comes from Finnish siisti, from Russian чи́стый, from Old East Slavic чистъ, from Proto-Slavic čistъ, from Proto-Balto-Slavic skīstas, from Proto-Indo-European skidtos, from Proto-Indo-European (s)keyd-.

Ancestry of “siistiys”, step by step

StepLanguageWordMeaning
1Finnishsiisticlean, neat; cool, wicked; Third-person singular...
2Russianчи́стыйclean
3Old East Slavicчистъpure; clean
4Proto-Slavicčistъclean, pure
5Proto-Balto-Slavicskīstas—
6Proto-Indo-Europeanskidtossplit
7Proto-Indo-European(s)keyd-—
Every word from Proto-Indo-European (s)keyd- →Every word from Proto-Indo-European skidtos →Every word from Proto-Balto-Slavic skīstas →