Fury a reader fails to finish (6)
I believe the answer is:
alecto
'fury' is the definition.
(I've seen this before)
'a reader fails to finish' is the wordplay.
'reader' becomes 'lector' (synonyms).
'fails to finish' means to remove the last letter.
'lector' with its last letter removed is 'lecto'.
'a'+'lecto'='ALECTO'
(Other definitions for alecto that I've seen before include "One of classical Furies" , "A fury; locate (anag.)" , "One of the Furies; locate (anag.)" , "Fury exhibited" , "Fury (Greek myth)" .)