Bone, thigh
The thigh bone in anatomy is called the 'femur.' Whichever term -- thigh bone or femur -- you care to use, it is the bone in the leg that extends from the hip to the knee.
The thigh bone/femur constitutes the entire upper leg, all of the leg <U>above</U> the knee.
As compared to the lower leg which boasts two bones (the tibia and the fibula), the upper leg has only one bone, the femur, but a very large bone it is, the largest in the human body.
The word 'femur' is the Latin word for thigh.