Neat, never knew that, I knew it wasn't Jewish - since we're a -ski but 100% Polish Roman Catholic on that side.-ski doesn't mean Jewish, it is (or was, thanks to communism) used to indicate nobility. Called a nobiliary particle in English. It's the Polish version of von (German) ven (Dutch) d' (French) or de (Italian). Though in those languages as well, it has come to mean "of" more than anything else.
Fun fact of the day. It changes based on gender.
Source: English teacher in Poland.