Knee

1. The joint between the thigh and the lower leg, formed by the articulation of the femur and the tibia and covered anteriorly by the patella.
2. An analogous joint or part of a leg of a quadruped vertebrate. The knees of racing horses take a lot of wear.
3. The part of a garment, as of trousers, that covers the knee. My work jeans have holes in the knees.