Related Clues:

• What a knockout!
• Sleep-inducing
• Wild blue yonder
• Old anesthetic
• Painkiller
• Sleep inducer
• Preoperative delivery, once
• It will knock you out
• Cousin of chloroform
• Part of the gasoline additive M.T.B.E.
• The heavens
• It's a gas?
• Soporific
• Inhalation anesthetic of old
• It's a gas!