zaći

1. (of the sun, moon) to set; to go down
   Sunce je već zašlo kad smo stigli. — The sun had already set when we arrived.
2. (za + acc.) to go behind; to disappear behind
   Auto je zašao za ugao i nestao. — The car went round the corner and disappeared.
   Mesec je zašao za oblak. — The moon went behind a cloud.
3. (u + acc.) to go deep into; to enter
   Zašli smo duboko u šumu i izgubili se. — We went deep into the forest and got lost.
   Već je zašla u četrdesete. — She's already into her forties.

The imperfective counterpart is zalaziti.