Two pieces in minor role (3,4)
I believe the answer is:
bit part
'minor role' is the definition.
(synonyms)
'two pieces' is the wordplay.
'two pieces' means two substitutions for 'piece'.
'piece' becomes 'bit' (synonyms).
'piece' becomes 'part' (synonyms).
'bit'+'part'='BIT-PART'
'in' is the link.
(Other definitions for bit part that I've seen before include "cameo" , "extra work, perhaps" , "Very minor role" , "Tiny or non-speaking dramatic role" , "Tool" .)