Small part arrived with ring attached (5)
I believe the answer is:
cameo
'small part' is the definition.
(small part in a film)
'arrived with ring attached' is the wordplay.
'arrived with' becomes 'came' (come can mean to appear or arrive. I am not sure about the 'with' bit.).
'ring' becomes 'O' (letter resembling a ring).
'attached' is a charade indicator (letters next to each other).
'came'+'o'='CAMEO'
(Other definitions for cameo that I've seen before include "Famous actor's small role" , "Brooch with an engraving in low relief" , "Item of jewellery with a portrait - distinguished actor's minor role" , "Small role in film" , "Small role for a well-known actor" .)