Uncredited actor (5)
I believe the answer is:
extra
'uncredited actor' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for extra that I've seen before include "Bolt-on" , "Minor actor in crowd scene" , "Cricket run; unusually" , "Bit actor in movie's crowd scenes" , "Run; in addition" .)