Writer is free at last, okay (9)
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I believe the answer is:
authorise
'okay' is the definition.
('okay'->'authorize' is in my internal thesaurus and 'ize'->'ise')
'writer is free at last' is the wordplay.
'writer' becomes 'author' (synonyms).
'at last' says to take the final letters.
The last letter of 'free' is 'e'.
'author'+'is'+'e'='AUTHORISE'
(Other definitions for authorise that I've seen before include "I share out (anag.)" , "Empower, permit" , "Give official permission to" , "OK" , "Sanction or establish officially" .)