Where does “poletni” come from?

poletni (Polish) comes from Polish lato, from Proto-Slavic lěto, from Proto-Indo-European leh₁tóm.

Ancestry of “poletni”, step by step

StepLanguageWordMeaning
1Polishlatosummer
2Proto-Slaviclětosummer; year
3Proto-Indo-Europeanleh₁tóm—
Every word from Proto-Indo-European leh₁tóm →Every word from Proto-Slavic lěto →Every word from Polish lato →