horsepower

Etymology

horse + power: the unit was originally defined as the amount of power that a horse could provide.

noun

1. (uncountable) Power derived from the motion of a horse.
   The wheel was to have been turned by horsepower, but it was adapted to be driven by a mill-wheel on the river Derwent […] 2003, Gavin Weightman, What the Industrial Revolution Did for Us, page 57
2. A nonmetric unit of power (symbol hp) with various definitions, for different applications. The most common of them is probably the mechanical horsepower, approximately equal to 745.7 watts.
   In the past, before the widespread adoption of SI units, the work that engines were capable of doing was compared with the work that horses could do – hence the term ‘horsepower’. Various people came up with various equivalencies, but the modern agreed definition is that 1 horsepower is 746 joules per second or 746 watts. 2012 March 22nd, David Blockley, Engineering: A Very Short Introduction (309), Oxford University Press, chapter 2: “The age of gravity – time for work”, page 20
3. A metric unit (symbol often PS from the German abbreviation), approximately equal to 735.5 watts.
4. (uncountable) Strength.
   political horsepower