Foul odor (6)
I believe the answer is:
stench
'foul odor' is the definition.
(I know that stench is a type of foul odor)
This is the entire clue.
(Other definitions for stench that I've seen before include "A really foul smell" , "Awful smell" , "Awful pong" , "Reek" , "Foul odour" .)