grueller

/ˈɡruːələr/
noun
  1. A person or thing that is extremely demanding, tiring, or difficult to deal with.
    • This hike is a grueller — we've been climbing for hours without a rest.
    • The new coach is a grueller who expects nothing less than perfection.
    • That final exam was a real grueller; hardly anyone finished on time.
Synonyms