The term 'PART OF HORSE'S FOOT' can be solved by the four-letter word 'HOOF'. A horse's HOOF is the hard outer covering of the foot of a horse, which is made up of a thick, horny, and keratinized layer of skin surrounding the distal phalanx of the 3rd toe of each of the four limbs of the horse. It is similar to a human fingernail or toenail, but more durable and more complex in structure. The HOOF is the end of the leg of the horse, and it is the only part of the horse that touches the ground when the horse is standing.