His part in a film may be superfluous (5)
I believe the answer is:
extra
'be superfluous' is the definition.
(synonyms)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for extra that I've seen before include "Maybe wide" , "Not a standard item" , "Bit actor in movie's crowd scenes" , "more than is necessary" , "Spare" .)