Fix a broken rapier (6)
I believe the answer is:
repair
'fix' is the definition.
(to fix something is to repair it)
'a broken rapier' is the wordplay.
'a broken' indicates anagramming the letters.
'rapier' anagrammed gives 'REPAIR'.
(Other definitions for repair that I've seen before include "Correct" , "Patch up" , "Restore (something) to good condition" , "Mend, put right" , "Proceed - restore" .)