'Adversary' in the Bible

Samuel said, "Why then do you ask of me, since Yahweh has departed from you and has become your adversary?

But the princes of the Philistines were angry with him; and the princes of the Philistines said to him, "Make the man return, that he may go back to his place where you have appointed him, and let him not go down with us to battle, lest in the battle he become an adversary to us. For with what should this fellow reconcile himself to his lord? Should it not be with the heads of these men?