Related Clues:

• [bo-o-o-ring!]
• Respond to a bore
• Give in to gravity
• Sign of aging
• Demonstrate boredom
• React to gravity
• [Ho-hum]
• Lose tautness
• Sink in the middle
• Become weary
• Lose tautness, in a way
• Yield to gravity
• Hint to an unexciting speaker
• Lose oomph
• Fall down