Queen inhabits excellent piece of land (4)
I believe the answer is:
acre
'piece of land' is the definition.
(I've seen this in another clue)
'queen inhabits excellent' is the wordplay.
'queen' becomes 'r' (abbreviation for regina, e.g. in ER ).
'inhabits' indicates putting letters inside.
'excellent' becomes 'ace' (ace can informally mean very good).
'r' placed within 'ace' is 'ACRE'.
(Other definitions for acre that I've seen before include "Imperial unit of area" , "Care about this bit of land" , "Site of battle" , "Middle East port" , "Unit of area - Israeli port" .)