Very small role (3,4)
I believe the answer is:
bit part
'very small role' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for bit part that I've seen before include "extra work, perhaps" , "Tiny or non-speaking dramatic role" , "'Small role in film or play (3,4)'" , "Very minor role" , "Small acting role" .)