Nonsense about former pupil being zombie! (5)
I believe the answer is:
robot
'zombie' is the definition.
Although both the answer and definition are singular nouns, I don't see how they can define each other.
'nonsense about former pupil' is the wordplay.
'nonsense' becomes 'rot' (rot can mean nonsense or rubbish).
'about' means one lot of letters goes inside another.
'former pupil' becomes 'OB' (abbreviation for 'Old Boy' - private school pupil).
'rot' going around 'ob' is 'ROBOT'.
'being' acts as a link.
Can you help me to learn more?
(Other definitions for robot that I've seen before include "Android, possibly" , "Factory worker, perhaps" , "Mechanism that can move like a human" , "performer lacking emotion" , "Automatic machine" .)