Son nudges mum, seen by new representative (9)
I believe the answer is:
spokesman
'representative' is the definition.
(spokesman is a kind of representative)
'son nudges mum seen by new' is the wordplay.
'son' becomes 's'.
'nudges' becomes 'pokes'.
'mum' becomes 'ma' (synonyms).
'seen by' means one lot of letters go next to another.
'new' becomes 'n' (common abbreviation eg NT for New Testament).
's'+'pokes'+'ma'+'n'='SPOKESMAN'
(Other definitions for spokesman that I've seen before include "One who makes statements for others" , "Voice" , "One speaking for others" , "wheelwright?" , "Representative at press conference" .)