Gain trade arrangement as a writer (9)
I believe the answer is:
tragedian
'a writer' is the definition.
(tragedian is a kind of writer)
'gain trade arrangement' is the wordplay.
'arrangement' indicates an anagram.
'gain'+'trade'='gaintrade'
'gaintrade' anagrammed gives 'TRAGEDIAN'.
'as' is the link.
(Other definitions for tragedian that I've seen before include "A great din (anag) - actor" , "actor in Macbeth?" , "Serious actor" , "Dramatist" , "Egad, I rant about actor in sad drama" .)