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 above 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.