Related Clues:

• Contain nitric oxide, symbolically described
• Short period of intense activity
• Fight; instance of illness
• Pay-per-view event, sometimes
• Boxing contest
• Enclose or surround completely
• Engagement ring
• (Drinking) session
• Ring for directions to theatre seats
• An exchange of blows, but there's nothing in it
• O to do this!
• Boxer's first to get unconscious in contest
• Fit for a spell
• Get around, having got rid of a bit of an illness
• Arc-en-ciel formed without a surround