Where does “бла́то” come from?

бла́то (Russian) comes from Church Slavonic блато, from Proto-Slavic bolto, from Proto-Balto-Slavic balta.

Ancestry of “бла́то”, step by step

StepLanguageWordMeaning
1Church Slavonicблато—
2Proto-Slavicboltoswamp; mud
3Proto-Balto-Slavicbalta—
Every word from Proto-Balto-Slavic balta →Every word from Proto-Slavic bolto →Every word from Church Slavonic блато →
бла́то — Etymology, Origin & Word History | Etymology Explorer