I was wondering about the ending -sk(+ optionally an additional vowel) used to create adjectives from names of the nations in Nordic (at least Danish and Swedish) as well as some Slavic languages (at least Polish and Croatian).
For example (the following lines are in format: English: Danish, Swedish, Croatian, Polish):
- Danish: Dansk, Danska, Dansk[i/a]*, Duńsk[i/a]*
- Polish: Polsk, Polska, Poljsk[i/a]*, Polsk[i/a]*
- English: Engelsk, Engelska, Englesk[i/a]*, Angielsk[i/a]*
* -i - masculine form, -a - feminine form. Not to add irrelevant details I didn't mention suffixes for neuter and plural forms.
Don't know about the other languages but in Polish -sk[i/a] is used also for some other adjectives:
- król (king) -> królewski/królewska (royal)
- papież (pope) -> papieski/papieska (papal)
- zielarz (herbalist) -> zielarski/zielarska (herbal)
- niebo (sky) -> niebieski/niebieska (blue)
And many surnames:
- kowal (blacksmith) -> Kowalski/Kowalska (the most popular Polish surname)
- jabłoń (apple-tree) -> Jabłoński/Jabłońska
- wiśnia (cherry) -> Wiśniewski/Wiśniewska
Is it something Proto-Indo-European, or it's just a coincidence? If it's a coincidence, how did it appear in Nordic languages? (If I'm not mistaken -ski ending was used already in Proto-Slavic.)