nemesis

noun (plural nemeses /-siːz/)

• the inescapable agent of someone’s or something’s downfall:injury, consistently his nemesis, struck him down during the match
• a long-standing rival; an arch-enemy:will Harry Potter finally defeat his nemesis, Voldemort?
• [mass noun] a downfall caused by an inescapable agent:one risks nemesis by uttering such words
• (often Nemesis) [mass noun] retributive justice:Nemesis is notoriously slow