Part of the film? (4)
I believe the answer is:
role
'part' is the definition.
(eg a theatrical role)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for role that I've seen before include "Duty" , "Part played (in life?)" , "Part in play, film etc" , "Part, portrayal" , "Playing part" .)