Meaning of “nemesis” in the English Dictionary. See all translations. uk ​ /ˈnem.ə.sɪs/ us ​ /ˈnem.ə.sɪs/ plural nemeses literary. › Someone's nemesis is a person or thing that is very difficult for them to defeat. › (a cause of) punishment or defeat that is deserved and cannot be avoided: The tax increases proved to be the president's political nemesis. Thesaurus: synonyms and related words.