Addresses nun restraining delayed Christian, who's an American filmstar (6)
I believe the answer is:
slater
'christian who's an american filmstar' is the definition.
I can't judge whether this definition defines the answer.
'addresses nun restraining delayed' is the wordplay.
'addresses nun' becomes 'sr' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'restraining' indicates putting letters inside.
'delayed' becomes 'late' (running late).
'sr' placed around 'late' is 'SLATER'.
Can you help me to learn more?
(Other definitions for slater that I've seen before include "High-up person" , "High-reaching worker perhaps" , "Man on top" , "Alerts (anag) - building worker" , "Does one abuse" .)