Surplus actor (5)
I believe the answer is:
extra
This clue is a double definition.
'surplus' is the first definition.
(I know that surplus can be written as extra)
'actor' is the second definition.
(extra is a type of actor)
(Other definitions for extra that I've seen before include "Supplemental" , "small-time actor" , "Small part actor" , "There's more" , "Left over" .)