pretpostavka

1. assumption; supposition
   Moja pretpostavka je da će zakasniti. — My assumption is that he'll be late.
   Pod pretpostavkom da sve prođe dobro, krećemo u petak. — Assuming everything goes well, we leave on Friday.
2. (za + accusative) prerequisite; precondition
   Dobro zdravlje je osnovna pretpostavka za uspeh. — Good health is the basic prerequisite for success.

Common set phrase: pod pretpostavkom da — "assuming that". In the sense "prerequisite" it takes za + accusative: pretpostavka za uspeh — a prerequisite for success.