Mend broken rapier (6)
I believe the answer is:
repair
'mend' is the definition.
(synonyms)
'broken rapier' is the wordplay.
'broken' is an anagram indicator.
'rapier' is an anagram of 'REPAIR'.
(Other definitions for repair that I've seen before include "Mend, restore to good condition" , "Restore (something) to good condition" , "remedy" , "Withdraw" , "Patch up" .)