Where does “trzechsetny” come from?

trzechsetny (Polish) comes from Polish trzy, from Proto-Slavic trьje, from Proto-Balto-Slavic tríjes, from Proto-Indo-European *tréyes.

Ancestry of “trzechsetny”, step by step

trzechsetny traces back through two separate lines of ancestry.

via Polish trzy

StepLanguageWordMeaning
1Polishtrzythree
2Proto-Slavictrьjethree
3Proto-Balto-Slavictríjesthree
4Proto-Indo-European*tréyes—

via Polish setny

StepLanguageWordMeaning
1Polishsetnyhundredth
2Proto-Slavic*sъtьnъ—
Every word from Proto-Indo-European *tréyes →Every word from Proto-Balto-Slavic tríjes →Every word from Proto-Slavic trьje →