Small mistake (4)
(Other definitions for lapse that I've seen before include "Slip; sounds like circuits" , "Retrogress" , "moral shortcoming" , "Pleas (anag)" , "Slight error as caused by inattention" .)
'small mistake' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for slip that I've seen before include "Minor error; garment" , "Lose footing as on banana skin" , "Slight mistake" , "Slight error" , "Minor error, stumble" .)