Boxer's weapon (4)
I believe the answer is:
fist
'boxer's weapon' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for fist that I've seen before include "handwriting?" , "or be decked in a ring" , "duke" , "Hit with a clenched one" , "Hand with the fingers clenched in the palm" .)