Put to death in river? Charming! (7)
I believe the answer is:
execute
'put to death' is the definition.
(synonyms)
'river? charming' is the wordplay.
'river?' becomes 'exe' (River Exe).
'charming' becomes 'cute' (I've seen this before).
'exe'+'cute'='EXECUTE'
'in' acts as a link.
(Other definitions for execute that I've seen before include "ice" , "shoot" , "Carry into effect" , "Discharge" , "Carry out; behead" .)