Where does “południejszy” come from?

południejszy (Polish) comes from Polish -ejszy, from Old Polish -ejszy, from Old Polish -szy, from Proto-Slavic *-jьjь.

Ancestry of “południejszy”, step by step

StepLanguageWordMeaning
1Polish-ejszyforms relational adjectives from temporal adverbs
2Old Polish-ejszyforms relational adjectives from temporal adverbs
3Old Polish-szyforms comparative adjectives; -er
4Proto-Slavic*-jьjь—
Every word from Proto-Slavic *-jьjь →Every word from Old Polish -szy →Every word from Polish -ejszy →