Hôrse'-pow'er, n.

n. 1. The power which a horse is capable of exerting.

2Sense 2. (Mach.) A unit or standard by which the capabilities of steam-engines and other prime-movers are measured; estimated as 33,000 pounds raised one foot in a minute.

☞ Work is an exertion of pressure through space. The unit by which quantities of work are measurable, is the labor necessary to raise one pound through the height of one foot. The rate at which work is done, is expressed in horse-power, and one horse-power is equivalent to the work done by continuous exertion at the rate of 33,000 lbs. raised through one foot in one minute; that is, to the performance of 33,000 units of work per minute. D. K. Clark. As a horse can exert such a force but six hours a day, one machinery horse-power is equivalent to that of 4.4 horses. Haswell. Nominal horse-power is a term still used in England to express certain proportions of cylinder, but of no value as a standard of measurement. The actual or indicated horse-power of an engine, is from three to five times the nominal horse-power; the elements of its calculation are the speed of the piston, and the pressure upon it as shown by the indicator-card, or as calculated by approximate rules. See INDICATOR-CARD.

3Sense 3. A machine operated by one or more horses; a horse-engine.