Hammer or wrench (4)
I believe the answer is:
tool
I believe this is a double definition.
'hammer' is the first definition.
(I've seen this in another clue)
'wrench' is the second definition.
(thesaurus)
(Other definitions for tool that I've seen before include "Cat's-paw; impress design on" , "Hand implement" , "Practical implement" , "Pawn" , "Appliance" .)