This writer's mature portrayal (5)
I believe the answer is:
image
'portrayal' is the definition.
(thesaurus)
'this writer's mature' is the wordplay.
'this writer's' becomes 'i'm' (referring to the person writing the clues).
'mature' becomes 'age' (synonyms).
'im'+'age'='IMAGE'
(Other definitions for image that I've seen before include "Likeness, could be spitting" , "Figure (of speech?)" , "Picture; simile" , "Likeness U symbol" , "Likeness of person or thing" .)