Bone below the femur (5)
I believe the answer is:
tibia
'bone below the femur' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tibia that I've seen before include "ancient pipe" , "Bone in osso bucco" , "Bone of the lower leg" , "The formal shinbone" , "part of skeleton" .)