A nemesis is an opponent or rival who seems perfectly matched against you, creating an ongoing challenge or conflict. A nemesis consistently stands in your way, almost as if they were designed specifically to test you, creating a relationship more intense and personal than ordinary competition.

In Greek mythology, Nemesis was the goddess of revenge and justice, which gives the word its serious weight. Today, we use it more broadly. A chess champion might have a nemesis who always plays the exact style that gives her trouble. A detective might spend years pursuing a criminal mastermind who becomes his nemesis. In stories, Batman's nemesis is the Joker, while Sherlock Holmes faces his intellectual equal in Professor Moriarty.

Your nemesis doesn't have to be an enemy in the dramatic sense. A math student might call fractions their nemesis if those problems consistently trip them up. A runner might consider a particular hill on the cross-country course their nemesis because it always slows them down.

The plural is nemeses (NEM-uh-seez). What makes someone a true nemesis is the sense that they’re perfectly designed to challenge you, pushing you to become better even as they frustrate your efforts.