Pass into disuse (5)
I believe the answer is:
lapse
'pass into disuse' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for lapse that I've seen before include "Slight error due to forgetfulness" , "Loss (in concentration, say?)" , "Cease to be valid" , "Slight error as caused by inattention" , "Pleas about omission" .)