seka

1. colloq. affect. sis; little sister
   Moja seka je upravo upisala fakultet. — My sis has just started university.
   Seko, dođi da ti nešto pokažem! — Sis, come here, I want to show you something!
2. colloq. affect. (as a form of address) girl; sis
   Seko, izgledaš sjajno večeras! — Girl, you look amazing tonight!

In direct address the vocative form seko is usually used.