Possible Clues:

• Circle line — a sensitive location for strike
• Husband in line for emotional response
• 'The Lost --', a song composed by Arthur Sullivan
• Triad, for example
• A musician may strike it
• C-E-G, e.g.
• It can't be played on a clarinet
• It may be struck
• Ninth, e.g.
• 'The Lost - - ' (Sullivan)