Book probing source subject of much SF (5)
I believe the answer is:
robot
'subject of much sf' is the definition.
I can't judge whether this defines the answer.
'book probing source' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'probing' indicates putting letters inside (probe can mean to poke or prod into).
'source' becomes 'root' (both can mean the origin of something).
'b' placed into 'root' is 'ROBOT'.
Can you help me to learn more?
(Other definitions for robot that I've seen before include "Computer-controlled machine" , "Unpaid worker" , "Factory worker, perhaps" , "Automatic worker?" , "Mechanical worker" .)