The term LEADING HORSE can be broken down into two words, PACER being the 5 letter solution. A PACER is a type of horse that is used in harness racing, where the horse pulls a two-wheeled cart called a sulky. Pacers are known for their smooth gait and speed, making them ideal for racing. They are also used in show rings and for pleasure riding. Pacers are usually bred for racing, and they are often the leading horse in a race.