Where does “сяно” come from?

сяно (Bulgarian) comes from Proto-Slavic sěno, from Proto-Balto-Slavic śáina, from Proto-Indo-European (s)ḱeh₁y- — to shine, shimmer.

Ancestry of “сяно”, step by step

StepLanguageWordMeaning
1Proto-Slavicsěnohay
2Proto-Balto-Slavicśáina—
3Proto-Indo-European(s)ḱeh₁y-to shine, shimmer

Words derived from “сяно”

Every word from Proto-Indo-European (s)ḱeh₁y- →Every word from Proto-Balto-Slavic śáina →Every word from Proto-Slavic sěno →