Local agent's ultimate green housing (6)
I believe the answer is:
native
'local' is the definition.
(similar in meaning)
'agent's ultimate green housing' is the wordplay.
'agent's ultimate' becomes 't' (I can't justify this - if you can you should give a lot more credence to this answer).
'green' becomes 'naive' (green can mean naive or innocent).
'housing' indicates putting letters inside.
't' placed within 'naive' is 'NATIVE'.
(Other definitions for native that I've seen before include "One born in a certain place" , "mother" , "Of person, belonging by birth to place" , "Resident" , "Local inhabitant" .)