A traitor enters river to get clear (9)
I believe the answer is:
exonerate
'clear' is the definition.
(to clear of criminal charges)
'a traitor enters river' is the wordplay.
'a' becomes 'one'.
'traitor' becomes 'rat' (I've seen this in another clue).
'enters' is an insertion indicator.
'river' becomes 'exe' (River Exe).
'one'+'rat'='onerat'
'onerat' placed inside 'exe' is 'EXONERATE'.
'to get' acts as a link.
(Other definitions for exonerate that I've seen before include "Release" , "let off the hook" , "Discharge" , "Free of duty" , "free of charge" .)