unija

1. union
   Srbija želi da postane članica Evropske unije. — Serbia wants to become a member of the European Union.
   Dve države su stvorile carinsku uniju. — The two countries formed a customs union.
2. (in mathematics) union of sets
   Unija skupova A i B sadrži sve njihove elemente. — The union of sets A and B contains all their elements.

A trade union is sindikat in Serbian, not unija.