monomaniac
/ˌmɑnoʊˈmeɪniˌæk/
noun
- A person who has an excessive or obsessive interest in a single subject or idea.
- My neighbor is a monomaniac for gardening; her yard is perfect year-round.
- The detective was a monomaniac when it came to solving cold cases.
- He's a monomaniac about fitness, spending every free hour at the gym.
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