Instrument George Michael and mate finally installed in apartment (9)
I believe the answer is:
flageolet
'instrument' is the definition.
(flageolet is a kind of instrument)
'george michael and mate finally installed in apartment' is the wordplay.
I cannot really see how this works, but
'george' could be 'geo' and 'geo' is found within the answer.
This explanation may well be incorrect...
(Other definitions for flageolet that I've seen before include "Instrument of the recorder family" , "Pipe" , "Type of recorder" , "Pulse" , "bean!" .)