Related Clues:

• Words of warning
• 'No kidding!'
• Stern
• Grave
• 'Don't play with me!'
• 'No kidding'
• Earnest
• 'This is no joke!'
• Somber
• Important
• 'You should listen to me'
• On the level
• 'Don't test me!'
• Parent's warning
• Solemn