Sci-fi author Asimov (5)
I believe the answer is:
isaac
'sci-fi author asimov' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for isaac that I've seen before include "Newton's first name" , "Biblical patriarch" , "- Newton, Eng. physicist and mathematician" , "Sacrificial offering" , "Youth almost sacrificed" .)