Concerning wrong reply (6)
I believe the answer is:
retort
'reply' is the definition.
(I know that retort is a more specific form of the action reply)
'concerning wrong' is the wordplay.
'concerning' becomes 're' (both can mean on a particular topic).
'wrong' becomes 'tort' (legal term).
're'+'tort'='RETORT'
(Other definitions for retort that I've seen before include "A quick, sharp reply" , "Part of chemist's equipment" , "Long-necked glass vessel" , "Chem. flask; sharp answer" , "Witty/sharp reply" .)