The term 'CAPPED PART' can be solved by the word 'KNEE', which is a four letter word. The KNEE is a joint in the body that connects the thigh and lower leg bones, and it is also the largest joint in the human body. It is a hinge joint that allows for movement in two directions, flexion and extension. The KNEE is also capped by the patella, or kneecap, which is a small, round bone that helps protect the KNEE joint.