Clear river containing single rodent (9)
I believe the answer is:
exonerate
'clear' is the definition.
(to clear of criminal charges)
'river containing single rodent' is the wordplay.
'river' becomes 'exe' (River Exe).
'containing' indicates putting letters inside.
'single' becomes 'one' (a single thing - only one).
'rodent' becomes 'rat' (rat is a kind of rodent).
'one'+'rat'='onerat'
'exe' going around 'onerat' is 'EXONERATE'.
(Other definitions for exonerate that I've seen before include "Acquit" , "Justify" , "Free from obligation, blame" , "Release" , "Clear of blame" .)