Small shack for tool (6)
I believe the answer is:
shovel
'tool' is the definition.
(shovel is a kind of tool)
'small shack' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'shack' becomes 'hovel' ('hovel' can be a synonym of 'shack').
's'+'hovel'='SHOVEL'
'for' acts as a link.
(Other definitions for shovel that I've seen before include "Tool for lifting and carrying" , "Tool like a spade" , "Old clerical hat" , "Scooper" , "Dig" .)