Modest abode originally, and not a landed estate (5)
I believe the answer is:
manor
'a landed estate' is the definition.
(manor is a kind of landed estate)
'modest abode originally and not' is the wordplay.
'originally' says to take the initial letters.
'and not' becomes 'nor' ('nor' means 'and also not').
The first letters of 'modest abode' is 'ma'.
'ma'+'nor'='MANOR'
(Other definitions for manor that I've seen before include "Police district (slang)" , "Grand but strange Roman house" , "house on estate" , "Landed estate" , "Large country house with lands" .)