defeater
/dɪˈfiːtə
/noun
A person or thing that defeats or conquers someone or something: the onset of hopelessness is the great defeater...
- This is a potential defeater for my being rational in accepting theistic belief.
- Even if I defeated myself, I would still exist as the defeater.
- Nimue is specifically named as a Lady of the Lake; she is the defeater, or perhaps simply replacer, of Merlin at Arthur's Court.