Stink to high heaven (4)
I believe the answer is:
reek
'stink to high heaven' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for reek that I've seen before include "Smell foully" , "Smell to high heaven" , "hum a lot!" , "'Stink, stench (4)'" , "Strong smell" .)