Where does “čьrxnъ” come from?

čьrxnъ (Proto-Slavic) comes from Proto-Slavic kьršnъ, from Proto-Balto-Slavic kiršnas, from Proto-Indo-European kr̥snós, from Proto-Indo-European kers- — black, dirty; run; to run.

Ancestry of “čьrxnъ”, step by step

StepLanguageWordMeaning
1Proto-Slavickьršnъ—
2Proto-Balto-Slavickiršnasblack
3Proto-Indo-Europeankr̥snósblack; dark, dusky
4Proto-Indo-Europeankers-black, dirty; run; to run
Every word from Proto-Indo-European kers- →Every word from Proto-Indo-European kr̥snós →Every word from Proto-Balto-Slavic kiršnas →