Sharp reply concerning new member duke introduced (9)
I believe the answer is:
rejoinder
'sharp reply' is the definition.
(I've seen this before)
'concerning new member duke introduced' is the wordplay.
'concerning' becomes 're'.
'new member' becomes 'joiner' (someone who has joined an organisation).
'duke' becomes 'd'.
'introduced' means one lot of letters goes inside another.
'joiner' placed around 'd' is 'joinder'.
're'+'joinder'='REJOINDER'
(Other definitions for rejoinder that I've seen before include "Quick comeback" , "Clever answer" , "Quick, witty reply" , "A sharp reply or retort" , "Response" .)