Smell extremely bad odour around layabout (4)
I believe the answer is:
slob
'layabout' is the definition.
(I've seen this before)
'smell extremely bad odour around' is the wordplay.
'extremely' says to hollow out the word (remove centre letters) (only the extremes of the word are used).
'bad odour' becomes 'BO' (short for body odour).
'around' says the letters should be written in reverse.
'smell' with its middle removed is 'sl'.
'bo' in reverse letter order is 'ob'.
'sl'+'ob'='SLOB'
(Other definitions for slob that I've seen before include "Couch potato" , "Sort of ice" , "Untidy and lazy person" , "Slovenly person (colloq.)" , "Fat, idle person" .)