An enemy is someone actively opposed to you, working against your interests or trying to harm you. In war, nations become enemies, with their armies fighting each other. In stories, the hero faces an enemy who wants to stop them or cause trouble: Voldemort is Harry Potter's enemy, the White Witch is the enemy of Narnia's true kings and queens.

But enemy doesn't only describe dramatic conflicts. On a playground, if someone keeps sabotaging your games or deliberately trying to hurt your feelings, they're acting like an enemy. The word suggests active opposition with intent to harm, different from simple disagreement or competition. Your opponent in chess isn't your enemy: you're both following the same rules and respecting each other. An enemy wants you to fail or suffer.

Sometimes people say things like “Mosquitoes are the enemy of a good camping trip” or “Procrastination is the enemy of success.” This means something that consistently works against what you're trying to accomplish.

The phrase “make an enemy of” means turning someone against you through your actions. If you betray a friend's trust, you might make an enemy of them. History shows that former enemies can become friends or allies, but rebuilding trust takes sincere effort and time.