Ostrich's Aussie cousin (3)
I believe the answer is:
emu
'ostrich's aussie cousin' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for emu that I've seen before include "Australian non-flyer" , "Physics unit" , "that doesn't get off the ground" , "Flightless bird of Australia, like ostrich" , "Large Australian flightless bird" .)