Related Clues:

• Tough to figure out
• Strenuous
• Tofu specification
• ___ as a diamond
• London meat pie
• Rock-like
• Grisham novel (with "The")
• Kind of rock or candy
• Unwilling to bend
• Like a Saturday crossword
• Flinty
• Fatiguing
• 10 on the Mohs scale
• Like some ciders
• Like some water or lemonade