Chief country with a prominent shoreline (8)
I believe the answer is:
headland
'a prominent shoreline' is the definition.
'chief country' is the wordplay.
'chief' becomes 'head' ('head' can be a synonym of 'chief').
'country' becomes 'land' ('land' can be a synonym of 'country'**).
'head'+'land'='HEADLAND'
'with' acts as a link.
(Other definitions for headland that I've seen before include "Cape" , "Promontory, territory jutting out into the sea" , "Promontory, area jutting out into the sea" , "Bill" , "Narrow promontory" .)