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