Law-breaking tool (3)
I believe the answer is:
awl
'tool' is the definition.
(awl is a kind of tool)
'law-breaking' is the wordplay.
'breaking' indicates anagramming the letters.
'law' anagrammed gives 'AWL'.
(Other definitions for awl that I've seen before include "Pointed tool used in leatherwork" , "Tool for hole making" , "it may be piercing" , "Cobbler's tool" , "Using sharp tool" .)