Cape in top nation (8)
I believe the answer is:
headland
'cape' is the definition.
(I've seen this before)
'top nation' is the wordplay.
'top' becomes 'head' (head is a kind of top).
'nation' becomes 'land' (synonyms).
'head'+'land'='HEADLAND'
'in' acts as a link.
(Other definitions for headland that I've seen before include "Promontory, area jutting out into the sea" , "Promontory, territory jutting out into the sea" , "Bill" , "Cape" , "Ness" .)