The English word adversary, meaning someone who opposes, is used to translate the Hebrew words of the Old Testament (pronounced) tsaw-rar, meaning to bind or cramp, and saw-tawn, from which originated the name Satan, which literally means adversary. In the New Testament, "adversary" is used to translate the Greek word (pronounced) anti-dee-kos, which means an opponent, including in reference to Satan, who made himself the primary opponent of God (see the Fact Finder question below), and in doing so also made himself the greatest fool, and the greatest loser, of all time.
"Adversary" was also used to describe people who opposed, or spoke against, someone else:
"And it came to pass, when Joshua was by Jericho, that he lifted up his eyes and looked, and, behold, there stood a man over against him with his sword drawn in his hand: and Joshua went unto him, and said unto him, Art thou for us, or for our adversaries?" (Joshua 5:13 KJV)
"But if you hearken attentively to his voice and do all that I say, then I will be an enemy to your enemies and an adversary to your adversaries." (Exodus 23:22 RSV)
"Thine hand shall be lifted up upon thine adversaries, and all thine enemies shall be cut off." (Micah 5:9 KJV)
"And when He [i.e. Jesus Christ] had said these things, all His adversaries were ashamed: and all the people rejoiced for all the glorious things that were done by Him" (Luke 13:17 KJV)
"Adversary" when used in reference to Satan:
"give none occasion to the adversary to speak reproachfully. For some are already turned aside after Satan." (1 Timothy 5:14-15 KJV)
"Humble yourselves therefore under the mighty hand of God, that in due time he may exalt you. Cast all your anxieties on him, for he cares about you. Be sober, be watchful. Your adversary the devil prowls around like a roaring lion [see also When The Cat Will Become The Mouse], seeking some one to devour. Resist him, firm in your faith, knowing that the same experience of suffering is required of your brotherhood throughout the world. And after you have suffered a little while, the God of all grace, Who has called you to His eternal glory in Christ, will Himself restore, establish, and strengthen you." (1 Peter 5:6-10 RSV)
Fact Finder: How did wicked Satan originate?
See Satan's Choice