Bone of a flightless bird with extremely fair skin (5)
I believe the answer is:
femur
'bone of a flightless bird' is the definition.
'femur' can be an answer for 'bone' (femur is a kind of bone). I'm not certain of the 'of a flightless bird' bit.
'with extremely fair skin' is the wordplay.
'with' indicates putting letters inside.
'extremely fair' becomes 'em' (I can't justify this - if you can you should believe this answer much more).
'skin' becomes 'fur' (fur is a kind of skin).
'em' put inside 'fur' is 'FEMUR'.
Can you help me to learn more?
(Other definitions for femur that I've seen before include "Longest bone in the human body" , "Bone in leg" , "Thigh bone" , "Large bone" , "Thighbone" .)