Where does “Kertšinsalmi” come from?

Kertšinsalmi (Finnish) comes from Finnish Salmi, from Finnish -lä, from Finnish -as, from Proto-Finnic -s, from Proto-Finno-Ugric -s.

Ancestry of “Kertšinsalmi”, step by step

Kertšinsalmi traces back through two separate lines of ancestry.

via Finnish Salmi

StepLanguageWordMeaning
1FinnishSalmiA town in Russian Karelia
2Finnish-läFront vowel variant of -la
3Finnish-asForms some adjectives; Forms some nouns
4Proto-Finnic-sForms nouns
5Proto-Finno-Ugric-s—

via Finnish Kertš

StepLanguageWordMeaning
1FinnishKertš—
2UkrainianКерч—
Every word from Proto-Finno-Ugric -s →Every word from Finnish -lä →Every word from Finnish -as →