an active opponent or enemy

Due to the wide variety of Army forces' missions across the full range of military operations, the term "adversary" is often used in this paper in lieu of enemy. The term enemy is reserved to indicate adversaries engaged in lethal operations against U.S. forces.

Adversaries are people who oppose each other in a conflict. They are also called opponents, parties, or disputants.

The opposing party in a lawsuit.

Opponent, the other party to the litigation.

An individual, group, organization or government that must be denied critical information. Synonymous with competitor/enemy.

The opponent in a case or the other party to a case.

The party opposite in a court action; the litigant-opponent.

Commonly used to refer to the opponent, the enemy, or any other mischievous person that desires to compromise one's security.

an opponent. The defendant is the plaintiff's adversary

In cryptography, an adversary (rarely opponent, enemy) is a malicious entity whose aim is to prevent the users of the cryptosystem from achieving their goal (primarily privacy, integrity and availability of data). An adversary's efforts might take the form of attempting to discover secret data, corrupting some of the data in the system, spoofing the identity of a message sender or receiver, or forcing system downtime.