Sci-fi author Isaac (6)
I believe the answer is:
asimov
'sci-fi author isaac' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for asimov that I've seen before include "He wrote about robots" , "Isaac -, US sci-fi writer" , "Isaac --, science fiction author" , "novelist" , "Isaac - - , SF writer" .)