Complex sentence: "Ski" (also "Sky" in other regions) is the formative adjective, continuation of Proto-Slavic language "", which defined affiliation to something, and was also used with names of territories and settlements to denote possession or place of origin.
Split into simpler sentences: Ski (also "Sky"in other regions) is a formative adjective, from the Proto-Slavic "", which defined affiliation to something. It was also used with names of territories and settlements to denote possession or place of origin.