Writer of ordinary book's nothing to Lorraine (6)
I believe the answer is:
obrien
'writer' is the definition.
(author Edna O'Brien)
'ordinary book's nothing to lorraine' is the wordplay.
'ordinary' becomes 'o' (abbreviation e.g. O-Levels).
'book' becomes 'b'.
'nothing to lorraine' becomes 'rien' ('nothing' in French - eg in the Lorraine region).
'o'+'b'+'rien'='OBRIEN'
'of' acts as a link.
(Other definitions for obrien that I've seen before include "Kate . . . . . ., Flann . . . . . . (1'5)" , "Irish writer" , "'Kate ..., Edna ..., (1'5)'" , "Flann -, Irish novelist" , "Edna, novelist" .)