Father holding big bird's thigh bone (5)
I believe the answer is:
femur
'thigh bone' is the definition.
(I've seen this before)
'father holding big bird's' is the wordplay.
'father' becomes 'fr' (abbreviation as in a priest's title).
'holding' is an insertion indicator.
'big bird' becomes 'emu' (type of large bird).
'fr' enclosing 'emu' is 'FEMUR'.
(Other definitions for femur that I've seen before include "Part of leg" , "Bone in leg" , "Thighbone" , "bit of leg" , "Longest bone in the human body" .)