'Opponent' in the Bible

As they grappled with one another, each one stabbed his opponent with his sword and they fell dead together. So that place is called the Field of Flints; it is in Gibeon.

The first to state his case seems right, until his opponent begins to cross-examine him.

and a sound message that cannot be criticized, so that any opponent will be at a loss, because he has nothing evil to say about us.