Largest bone in the body (5)
I believe the answer is:
femur
'largest bone in the body' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for femur that I've seen before include "Longest bone in the human body" , "Large bone" , "Thighbone" , "Thigh bone" , "Part of leg" .)