gasiti

1. (of a light, device) to turn off; to switch off
   Uvek gasim svetlo kad izlazim iz sobe. — I always turn off the light when I leave the room.
   Zašto ne gasiš televizor kad ideš na spavanje? — Why don't you turn off the TV when you go to bed?
2. (of fire) to put out; to extinguish
   Vatrogasci još uvek gase požar. — The firefighters are still putting out the fire.
   On gasi cigaretu u pepeljari. — He's stubbing out his cigarette in the ashtray.
3. (of a business) to shut down; to close down
   Firma gasi nekoliko prodavnica u Beogradu. — The company is closing down several stores in Belgrade.
4. (of thirst) to quench; to slake
   Hladna voda najbolje gasi žeđ. — Cold water quenches thirst best.
5. (gasiti se) to go out; to switch off
   Telefon mi se stalno gasi. — My phone keeps switching off.
   Vatra se polako gasila. — The fire was slowly dying out.

For lights Serbians usually say "gasiti/paliti"; for devices both pairs are used, "gasiti/paliti" and "isključivati/uključivati", depending on the device and context.