Mislay sole arrangement (4)
I believe the answer is:
lose
'mislay' is the definition.
(synonyms)
'sole arrangement' is the wordplay.
'arrangement' is an anagram indicator.
'sole' is an anagram of 'LOSE'.
(Other definitions for lose that I've seen before include "Shake off (a pursuer)" , "Fail to win" , "Fail to keep" , "Misplace" , "Don't win" .)