Where does “bratří” come from?

bratří (Czech) comes from Old Czech bratřie, from Proto-Slavic *bratrьja — collective brothers, brethren.

Ancestry of “bratří”, step by step

StepLanguageWordMeaning
1Old Czechbratřiebrethren, brothers
2Proto-Slavic*bratrьjacollective brothers, brethren
Every word from Proto-Slavic *bratrьja →Every word from Old Czech bratřie →