Attribute of a writer (7)
I believe the answer is:
ascribe
'attribute' is the definition.
(I know that attribute can be written as ascribe)
'a writer' is the wordplay.
'writer' becomes 'scribe' (scribe is a kind of writer).
'a'+'scribe'='ASCRIBE'
'of' acts as a link.
(Other definitions for ascribe that I've seen before include "Attribute in Brescia" , "'Attribute, assign (7)'" , "'Impute, assign (7)'" , "Attribute or impute" , "Attribute (something to a cause)" .)