Related Clues:

• Trying
• Difficult
• Backbreaking
• Demanding
• Burdensome
• Laborious
• Herculean
• Requiring great effort
• "Tough day, ___?"
• Strenuous
• Punishing
• Requiring much effort
• It's hard to make such a dour mixture with us
• Work that's so hard may make one dour in the USA
• No walk in the park