Sustained robin finally, one trapped in your and my outhouse (9)
I believe the answer is:
nourished
'sustained' is the definition.
('nourish' can be a synonym of 'sustain')
'robin finally one trapped in your and my outhouse' is the wordplay.
'finally' indicates one should take the final letters.
'one' becomes 'i' (Roman numeral).
'trapped in' indicates putting letters inside.
'your and my' becomes 'our' (I've seen this in another clue).
'outhouse' becomes 'shed' (a shed is an outside building).
The last letter of 'robin' is 'n'.
'our'+'shed'='ourshed'
'i' inserted within 'ourshed' is 'ourished'.
'n'+'ourished'='NOURISHED'
(Other definitions for nourished that I've seen before include "properly fed" , "Sustained" .)