doomster

/ˈdumstər/
noun
  1. A person who predicts disaster or bad things will happen, often in an exaggerated way.
    • The economist was called a doomster for predicting a market crash.
    • Doomsters on social media often spread panic about the future.
    • Every time there's a storm, my uncle becomes a doomster and warns everyone to prepare for the worst.
Antonyms