the power which a horse exerts.-a unit of power, used in stating the power required to drive machinery, and in estimating the capabilities of animals or steam engines and other prime movers for doing work. it is the power required for the performance of work at the rate of 33,000 english units of work per minute; hence, it is the power that must be exerted in lifting 33,000 pounds at the rate of one foot per minute, or 550 pounds at the rate of one foot per second, or 55 pounds at the rate of ten feet per second, etc.-a machine worked by a horse, for driving other machinery; a horse motor.