noun
nemesis
NEM-uh-sis/ˈneməsɪs/
A long-standing opponent who repeatedly causes defeat.
The composed opponent is the chess player's nemesis, defeating him in every encounter.

Etymology
Greek nemesis expressed the distribution of what was due, especially divine retribution, personified as a goddess. From this sense of inescapable reckoning came the modern nemesis: a rival or force that seems destined to defeat someone.
In context
Kua is a true nemesis. Not just a powerful enemy, but a dark reflection of our hero.
More examples
- Even after months of practice, I lose to my chess nemesis.
- She finally beats her nemesis after five straight losses.
- The two runners become his nemeses, beating him race after race.
Forms
nemesis · nemeses
Similar words
- rival
- Competes for the same goal without necessarily causing repeated defeats.
- archenemy
- Emphasizes deep hostility rather than a record of repeated victories.