Extinct flightless bird (3)
I believe the answer is:
moa
'extinct flightless bird' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for moa that I've seen before include "was hunted by Maori" , "Extinct flightless bird of New Zealand" , "Old bird" , "Bird's gone for ever" , "Bird that died out" .)