Your archenemy is your main enemy — the one you treat as the biggest opposite, not merely someone you dislike this week. Stories, comics, and games love the word: the hero has an archenemy. In real life it often sounds a little big and playful, so adults may smile when they use it (“my archenemy at tennis”). It can be a person, a group, or even a thing you always fight. You will also see arch-enemy with a hyphen, and older writing with a space; they mean the same thing. It is stronger than rival (a rival can still be friendly) and more story-like than enemy alone.

死敵；頭號敵人