'Adversary' in the Bible

But the Philistine commanders were angry with Achish and they said to him, “Make this man return, so that he may go back to his place where you have assigned him, and do not let him go down to battle with us, or in the battle he may [turn and] become our adversary. For how could David reconcile himself to his lord [Saul]? Would it not be with the heads of these [Philistine] men?