'Adversary' in the Bible

Samuel said, “Why then do you ask me, since the Lord has departed from you and has become your adversary?

But the commanders of the Philistines were angry with him, and the commanders of the Philistines said to him, “Make the man go back, that he may return 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 become an adversary to us. For with what could this man make himself acceptable to his lord? Would it not be with the heads of these men?