Our group pursuing smell to find decomposing matter (5)
I believe the answer is:
humus
'decomposing matter' is the definition.
(I've seen this before)
'our group pursuing smell' is the wordplay.
'our group' becomes 'us'.
'pursuing' is a charade indicator (letters next to each other).
'smell' becomes 'hum' (something with a bad smell is 'humming').
'us' after 'hum' is 'HUMUS'.
'to find' is the link.
(Other definitions for humus that I've seen before include "Partially decomposed matter in the soil" , "decomposing organic matter" , "Soil's organic component" , "Organic stuff" , "Decomposed vegetation" .)