Part of Australia (3,5,5)
I believe the answer is:
new south wales
'part of australia' is the definition.
('New South Wales' is part of 'australia')
This is the entire clue.
(Other definitions for new south wales that I've seen before include "Australian state, capital Sydney" , "Name given to Australia when colonised in 1788; a state since 1901" , "Sydney's state" .)