Partway through study characterising compost heap (6)
I believe the answer is:
midden
'compost heap' is the definition.
'partway through study' is the wordplay.
'partway through' becomes 'mid'.
'study' becomes 'den' (I've seen this before).
'mid'+'den'='MIDDEN'
'characterising' acts as a link.
(Other definitions for midden that I've seen before include "A heap of dung or rubbish heap" , "Manure heap" , "Refuse heap" .)