Large Australian flightless bird (3)
I believe the answer is:
emu
'large australian flightless bird' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for emu that I've seen before include "Australian non-flyer" , "Large Australian flightless bird" , "Fast runner in Oz" , "Australian bird related to the ostrich" , "Big bird" .)