stožer

1. formal (figuratively) mainstay; pillar; backbone
   On je stožer odbrane našeg tima. — He is the backbone of our team's defence.
   Porodica je bila stožer njegovog života. — Family was the pillar of his life.
2. pivot; pole
   Kapija se okreće oko gvozdenog stožera. — The gate turns on an iron pivot.

For "headquarters" Serbian uses štab (krizni štab); stožer in that sense is Croatian.