This is the 504th most frequent Croatian word.
sumnje
"Doubts" or "suspicions."
Here, 'sumnji' is used in the genitive plural form to convey the absence of doubt about someone's abilities.
Nemam nikakvih sumnji u tvoje sposobnosti.
I have no doubts about your abilities.
The word 'sumnja' is used as a subject in its singular nominative form to signify a general concept.
Sumnja je početak mudrosti.
Doubt is the beginning of wisdom.
In this sentence, 'sumnji' is employed in the genitive plural form to indicate the cause of someone's doubts.