adversary, enemy

Definition:

An "adversary" is a person or group who is opposed to someone or something. The term "enemy" has a similar meaning.

An adversary can be a person who tries to oppose you or harm you.
A nation can be called an "adversary" when it fights against another nation.
In the Bible, the devil is referred to as an "adversary" and an "enemy."
Adversary may be translated as "opponent" or "enemy," but it suggests a stronger form of opposition.