garant

1. colloq. for sure; definitely; guaranteed
   Garant će opet zakasniti, znaš ga. — He'll definitely be late again, you know him.
   Ako padne kiša, garant nema utakmice. — If it rains, there's definitely no match.

2. guarantor
   Ustav je garant ljudskih prava. — The constitution is the guarantor of human rights.
   Otac mu je bio garant za kredit. — His father was the guarantor for his loan.

In speech garant is very common as 'for sure'; a loan guarantor is more often called žirant.