psina

1. big dog; huge dog
   Komšija ima neku ogromnu psinu u dvorištu. — The neighbour has some huge dog in his yard.
   Ta psina laje celu noć. — That big dog barks all night.
2. colloq. (napraviti nekome psinu) dirty trick; prank
   Napravili su mu psinu i sakrili mu auto. — They played a dirty trick on him and hid his car.
   To nije bila šala, to je bila prava psina. — That wasn't a joke, that was a real dirty trick.

The word is feminine even though it refers to any dog: velika psina.