The Collaborative International Dictionary of English v.0.48:

knish \knish\ (k'n[i^]sh"), n. (Russian and Jewish Cookery)
   A fried, or sometimes baked, turnover made from a round or
   square sheet of dough containing a filling, usually of meat
   or potatoes.
   [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

knish
    n 1: (Yiddish) a baked or fried turnover filled with potato or
         meat or cheese; often eaten as a snack