This is the 773rd most frequent Croatian word.
protivnika
"Protivnika" in English means "opponent" or "adversary."
Here, 'Protivnik' is in the nominative case, serving as the subject of the sentence and identifying the one performing an action or described.
Protivnik u šahu je bio vrlo vješt igrač.
The opponent in chess was a very skilled player.
The word 'protivnika' here is used in the accusative case to denote the direct object 'the opponent' whom the action (defeated) was directed at.
Na utakmici smo pobijedili protivnika.
In the match, we defeated the opponent.
The word 'protivnikom' appears in the instrumental case, indicating that the action of 'debated' involved 'the opponent' as a partner in the action.