lija

1. colloq. (in fairy tales, folk speech) fox
   U basni lija prevari gavrana. — In the fable, the fox tricks the raven.
2. colloq. (of a person) sly fox; cunning person
   Pazi se njega, to je stara lija. — Watch out for him, he's a sly old fox.

The neutral word is lisica; lija sounds folksy or colloquial.