Appeared ordinary in small role (5)
I believe the answer is:
cameo
'small role' is the definition.
(I've seen this before)
'appeared ordinary' is the wordplay.
'appeared' becomes 'came' (I've seen this before).
'ordinary' becomes 'o' (abbreviation e.g. O-Levels).
'came'+'o'='CAMEO'
'in' acts as a link.
(Other definitions for cameo that I've seen before include "Brooch with an engraving in low relief" , "Item of jewellery with a portrait - distinguished actor's minor role" , "Medallion with a profile carved in relief" , "Small role - gem with a figure carved in relief" , "Carved brooch - small role" .)