Having estates secured (6)
I believe the answer is:
landed
'having' is the definition.
(thesaurus)
I don't understand the remainder of the clue.
Can you help me to learn more?
(Other definitions for landed that I've seen before include "Disembarked - owning estates" , "Came down to earth" , "Owning great estates" , "Alit; having estates" , "Came ashore" .)