Surplus actor in small role (5)
I believe the answer is:
extra
This clue might be a double definition.
'surplus' is the first definition.
(synonyms)
'actor in small role' is the second definition.
'extra' can be an answer for 'actor' (extra is a type of actor). I'm unsure of the 'in small role' bit.
Can you help me to learn more?
(Other definitions for extra that I've seen before include "Minor actor in crowd scene" , "Auxiliary" , "Bit player in film" , "late edition" , "redundant > spear-carrier" .)