Two components have minor role (3,4)
I believe the answer is:
bit part
'minor role' is the definition.
(synonyms)
'two components' is the wordplay.
'two components' means two substitutions for 'component'.
'component' becomes 'bit'.
'component' becomes 'part' (a component is a part of something).
'bit'+'part'='BIT-PART'
'have' acts as a link.
(Other definitions for bit part that I've seen before include "cameo" , "Tool" , "Very minor role" , "Small acting role" , "extra work, perhaps" .)