The word 膝盖 is formed through a vivid conceptual combination: the first character, 膝, means "knee" itself, referring to the joint, while the second character, 盖, means "cover" or "lid". Together, they create the image of the kneecap, the patella, as the bony cover or shield that sits over and protects the front of the knee joint, perfectly picturing the body part's structure and function.