The term 'Part of a Horse's Foot' can be broken down into two crossword solutions: HOOF (4 letters) and Pastern (7 letters). A HOOF is the hard, protective covering on the bottom of a horse's foot. It is made up of keratin, the same material that makes up human fingernails. The pastern is the area between the HOOF and the fetlock joint, which is the joint connecting the lower leg to the HOOF. It is made up of cartilage and is more flexible than the HOOF.