Related Clues:

• Drop round to see one off
• Slip, keel over, pass away
• Error made by student before recess
• Run out (of time?)
• Passing - mistake
• Decline - pass away
• Untypical mistake
• Fall from usual standard
• Temporary drop in standard
• Loss (in concentration, say?)
• Fall from the faith
• Sepal (anag)
• Expire, as an insurance policy
• Does this lapse refer to where old Nelson stood, say?
• Senior moment, e.g