Father holding Australian bird's bone (5)
I believe the answer is:
femur
'bone' is the definition.
(femur is a kind of bone)
'father holding australian bird's' is the wordplay.
'father' becomes 'fr'.
'holding' means one lot of letters goes inside another.
'australian bird' becomes 'emu' (I've seen this before).
'fr' going around 'emu' is 'FEMUR'.
(Other definitions for femur that I've seen before include "Bone in leg" , "Thigh bone" , "Thighbone" , "bit of leg" , "Longest bone in the human body" .)