Android book - Foundation - is enthralling (5)
I believe the answer is:
robot
'android' is the definition.
(I've seen this before)
'book foundation is enthralling' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'foundation' becomes 'root' (I've seen this in another clue).
'is enthralling' means one lot of letters goes inside another.
'b' put within 'root' is 'ROBOT'.
(Other definitions for robot that I've seen before include "Factory worker, perhaps" , "Programmed machine" , "Mechanism that can move like a human" , "performer lacking emotion" , "Soulless worker" .)