Bad smell (4)
'bad smell' is the definition.
(pong can informally mean a bad smell)
This is the entire clue.
(Other definitions for pong that I've seen before include "It may make one wrinkle nose" , "Reek" , "Stench" , "Nasty smell (informal)" , "In slang, a real stink" .)
(Other definitions for odor that I've seen before include "Pong in Ohio" , "Stink in US" .)
'bad smell' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for stench that I've seen before include "Strong unpleasant smell" , "Horrid smell" , "A really vile smell" , "Dreadful pong" , "Reek" .)