Tool in small shed (6)
I believe the answer is:
shovel
'tool' is the definition.
(I know that shovel is a type of tool)
'small shed' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'shed' becomes 'hovel' (both can mean a basic outdoor building).
's'+'hovel'='SHOVEL'
'in' acts as a link.
(Other definitions for shovel that I've seen before include "Tool for scooping" , "Tool like a spade" , "Digging implement" , "Excavator" , "''Don't forget your..., if you want to go to work'' (Christy Moore)" .)