Son with peers formulated reply (8)
I believe the answer is:
response
'reply' is the definition.
(I know that response is a type of reply)
'son with peers formulated' is the wordplay.
'with' means one lot of letters go next to another.
'formulated' is an anagram indicator (another formulation of the same letters).
'son' put after 'peers' is 'peersson'.
'peersson' is an anagram of 'RESPONSE'.
(Other definitions for response that I've seen before include "Answer - retort" , "bid by partner" , "Acknowledgement" , "See porn (anag) -- answer" , "Rejoinder, retort" .)