Repair form of weapon (6)
I believe the answer is:
rapier
'weapon' is the definition.
(rapier is a kind of weapon)
'repair form' is the wordplay.
'form' indicates an anagram (another form of the letters).
'repair' is an anagram of 'RAPIER'.
'of' acts as a link.
(Other definitions for rapier that I've seen before include "Light sword" , "Thin sharp sword" , "A fencing sword for repair" , "fencing equipment" , "A thin double-edged sword" .)