Femur and Thigh

Femur noun - The longest and thickest bone of the human skeleton; extends from the pelvis to the knee.

Thigh is a synonym for femur in hip joint topic. In some cases you can use "Thigh" instead a noun "Femur".

Thigh noun - The part of the leg between the hip and the knee.

Femur is a synonym for thigh in hip joint topic. You can use "Femur" instead a noun "Thigh", if it concerns topics such as leg part.