Related Clues:

• Inside diameter, as of a gun
• Betray boredom
• Death of the party?
• Windbag
• Ear bender
• Cause of ennui
• Gun-barrel diameter
• Inside tube diameter
• Demonstrate boredom, perhaps
• Dullsville denizen
• Act sleepy
• Be tedious
• Tube diameter
• Make sleep
• Reaction to an unexciting speaker