Brewer's: Hackney Horses
Not thoroughbred, but nearly so. They make the best roadsters, hunters and carriage horses; their action is showy, and their pace good. A first-class roadster will trot a mile in 2 minutes. Some American trotters will even exceed this record. The best hackneys are produced from thoroughbred sires mated with halfbred mares. (French, haguenée; the Romance word haque =the Latin equus; Spanish, hacanéa.)
In ordinary parlance, a hackney, hackney-horse, or hack, means a horse “hacked out” for hire. These horses are sometimes vicious private horses sold for “hacks” or worn-out coach-horses, and cheap animals with broken wind, broken knees, or some other defect.
“The knights are well horsed and the common people and others on litell hukeneys hackneys and geldynges.” —Froissart.