Prime minister? (8)
I believe this is a double definition.
'prime' is the first definition.
(I've seen this before)
'minister?' is the second definition.
(I know that cardinal is a type of bishop)
(Other definitions for cardinal that I've seen before include "Type of number or prelate" , "Most important number" , "of prime importance" , "papal adviser" , "fundamental importance" .)
'prime minister' is the definition.
(synonyms)
This is the entire clue.
(Other definitions for premier that I've seen before include "Foremost" , "First (minister)" , "Prime minister" , "Chief minister" , "PM" .)