Related Clues:

• Dull fellow
• Barrel's inside diameter
• Gun barrel diameter
• Unwanted guest, maybe
• One who goes on and on
• Tidal wave
• Put to sleep, so to speak
• Tedious fellow
• One causing ennui
• Drill holes
• Make weary by being dull
• Yawn producer, perhaps
• Make weary
• Yawn-inducing speaker, e.g.
• Dull person