središnji

1. central; middle
   Središnji deo grada je zatvoren za saobraćaj. — The central part of the city is closed to traffic.
2. key; main; central
   Središnja tema knjige je porodica. — The central theme of the book is family.
   Ona ima središnju ulogu u ovom projektu. — She has a key role in this project.

In everyday speech in Serbia centralni is more common.