A writer's attribute (7)
I believe the answer is:
ascribe
'attribute' is the definition.
('ascribe' can be a synonym of 'attribute')
'a writer's' is the wordplay.
'writer' becomes 'scribe' (scribe is a kind of writer).
'a'+'scribe'='ASCRIBE'
(Other definitions for ascribe that I've seen before include "Attribute or credit to" , "Attribute to, say, an old writer?" , "Attribute (something to a cause)" , "put down" , "Attribute or impute" .)