köken: Etymology tree Proto-Indo-European *kʷ- Proto-Indo-European *kʷís Proto-Indo-European *kʷídder. Proto-Slavic *česo Old Polish co Proto-Indo-European *ḱe Proto-Indo-European *ís Proto-Indo-European *ḱís Proto-Balto-Slavic *śís Proto-Slavic *sьder. Old Polish -ś Old Polish coś Polish coś Inherited from Old Polish coś. By surface analysis, co + -ś. Compare Kashubian cos and Slovincian cesz.