Father holding large bird’s leg bone (5)
I believe the answer is:
femur
'leg bone' is the definition.
(femur is a kind of leg bone)
'father holding large bird's' is the wordplay.
'father' becomes 'fr' (abbreviation as in a priest's title).
'holding' means one lot of letters goes inside another.
'large bird' becomes 'emu' (I've seen this in another clue).
'fr' placed around 'emu' is 'FEMUR'.
(Other definitions for femur that I've seen before include "bit of leg" , "Thighbone" , "Part of leg" , "Large bone" , "Thigh bone" .)