Where does “trzeciak” come from?
trzeciak (Polish) comes from Polish trzeci, from Old Polish trzeci, from Proto-Slavic tretь, from Proto-Balto-Slavic tretias, from Proto-Balto-Slavic tirtias, from Proto-Indo-European tr̥tyos, from Proto-Indo-European *tréyes.
Ancestry of “trzeciak”, step by step