Discharge is horribly near to blocking Devon river (9)
I believe the answer is:
exonerate
'discharge' is the definition.
(I know that discharge can be written as exonerate)
'horribly near to blocking devon river' is the wordplay.
'horribly' indicates anagramming the letters (a horribly wrong version of the letters).
'blocking' means one lot of letters goes inside another (block can mean to plug a gap in something).
'devon river' becomes 'exe' (I've seen this before).
'near'+'to'='nearto'
'nearto' anagrammed gives 'onerat'.
'onerat' put into 'exe' is 'EXONERATE'.
'is' is the link.
(Other definitions for exonerate that I've seen before include "Free of duty" , "Release" , "Discharge" , "let off the hook" , "Declare to be free from blame" .)