Again couple mend (6)
I believe the answer is:
repair
'mend' is the definition.
(I know that mend can be written as repair)
'again couple' is the wordplay.
'again' becomes 're' (prefix meaning 'again').
'couple' becomes 'pair' (synonyms).
're'+'pair'='REPAIR'
(Other definitions for repair that I've seen before include "It may be effected by" , "Make good again" , "Patch up" , "darn?" , "Restore; go" .)