Where does “čísti” come from?
čísti (Old Czech) comes from Proto-Slavic *čistì, from Proto-Balto-Slavic (s)keistéi, from Proto-Indo-European *(s)kʷéyt-t ~ *(s)kit-ént, from Proto-Indo-European kʷeyt- — to notice; to read.
Ancestry of “čísti”, step by step