Related Clues:

• Serene
• Library sign
• Restrained
• Hardly loquacious
• Hush
• Hushed
• Close-lipped
• 'Zip it!'
• Self-effacing
• Unwilling
• Much like Marcel Marceau
• 'Put a sock in it!'
• Angry teacher's cry
• Not saying much
• "Put a sock in it!"