Development of eastern nation (6)
I believe the answer is:
Here is my best explanation:
'development' is the definition.
'eastern nation' is the subsidiary indication.
'eastern' becomes 'e'.
'nation' becomes 'state' ('state' can be a synonym of 'nation').
'of' is the link.
(Other definitions for estate that I've seen before include "Large piece of land with a large house", "All of one's assets after death", "Extent of one's property", "The whole of one's possessionsat death", "Scheme of new housing", "Park it", "Rank - housing development - what's left in a will", "Possessions at the time of death", "Desmene" and "The whole of a deceased person's assets".)