Unfortunate smell passes main parts (6)
I believe the answer is:
bodies
'main parts' is the definition.
(the body of something is its main part)
'unfortunate smell passes' is the wordplay.
'unfortunate smell' becomes 'bo' (short for body odour).
'passes' becomes 'dies'.
'bo'+'dies'='BODIES'
(Other definitions for bodies that I've seen before include "See 12" , "people" , "Corpses or organisations" .)