If dodgy on the quiet, may be in bad odour (4)
I believe the answer is:
fish
'be in bad odour' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'if dodgy on the quiet' is the wordplay.
'dodgy' is an anagram indicator.
'on' is a charade indicator (letters next to each other).
'the quiet' becomes 'sh'.
'if' with letters rearranged gives 'fi'.
'fi'+'sh'='FISH'
'may' acts as a link.
Can you help me to learn more?
(Other definitions for fish that I've seen before include "Aquatic creature(s)" , "Possibly the sole" , "Eg, sturgeon" , "Aquatic animal(s)" , "Trawler's catch" .)