Repressed writer with backward set (4-2)
I believe the answer is:
pent-up
'repressed' is the definition.
(I know that repressed can be written as pent-up)
'writer with backward set' is the wordplay.
'writer with' becomes 'pen' (I've seen this in other clues).
'backward' is a reversal indicator.
'set' becomes 'put' (synonyms).
'put' reversed gives 'tup'.
'pen'+'tup'='PENT-UP'
(Other definitions for pent-up that I've seen before include "Closely confined" , "Repressed, emotions say" , "Confined like dam water or suppressed anger" , "Held back, confined" , "Confined like feelings or water behind dam" .)