Related Clues:

• Peremptory signal
• Quiet "Quiet!"
• "That's enough from you!"
• Warning that often precedes 17-, 30-, 49- and 65-Across
• Gag order?
• 'Not a word!'
• 'No noise!'
• 'Not another peep!'
• Theater sound
• Theater reproof
• "Quiet down!"
• Silencer's sound
• Librarian's rebuke
• 'I don't want to hear another word!'
• A sound for silence