Stench in river preceding alarmed response (4)
I believe the answer is:
reek
'stench' is the definition.
(synonyms)
'river preceding alarmed response' is the wordplay.
'river' becomes 'r' (abbreviation).
'preceding' means one lot of letters go next to another.
'alarmed response' becomes 'eek' (I can't justify this - if you can you should give a lot more credence to this answer).
'r'+'eek'='REEK'
'in' acts as a link.
Can you help me to learn more?
(Other definitions for reek that I've seen before include "Effluvium" , "Smell offensively" , "Smell bad" , "Emit smoke" , "Smell to high heaven" .)