Soil fungus? (5)
I believe the answer is:
mould
I believe this is a double definition.
'soil' is the first definition.
(mould is a kind of soil)
'fungus?' is the second definition.
(mould is a kind of fungus)
(Other definitions for mould that I've seen before include "Must" , "Fungal growth; template" , "Crumbly soil" , "development of earth" , "Cause of discoloration" .)