Nation applying old tax to estate (8)
I believe the answer is:
scotland
'nation' is the definition.
(Scotland is an example)
'old tax to estate' is the wordplay.
'old tax' becomes 'scot' (I've seen this before).
'to estate' becomes 'land' (synonyms).
'scot'+'land'='SCOTLAND'
'applying' acts as a link.
(Other definitions for scotland that I've seen before include "North of the border" , "Alban" , "Semi-autonomous region of the UK" , "The thistle is its emblem" , "The country of strange cold ants" .)