In the history of thermodynamics, motive power is a term used to signify the work energy associated with lifting a weight through a height. The term was defined by French physicist Sadi Carnot, in his 1824 memoir On the Motive Power of Fire, where he stated that:

“We use here the expression motive power to express the useful effect that a motor is capable of producing. This effect can always be likened to the elevation of a weight to a certain height. It has, as we know, a measure, the product of the weight multiplied by the height to which it is raised.”

This equation is:

Motive power = weight ∙ height

In modern terms, this is the standard definition of work:

Work = mgh

History
Prior to Carnot, the term "motive power" was first used, in a mechanical sense, in the 1690 publication “A New Method to Obtain Very Great Motive Powers at Small Cost” by French engineer Denis Papin, in which contained the first prototype design a steam engine. [2]

References
1. Carnot, Sadi. (1824). “Reflections on the Motive Power of Fire and on Machines Fitted to Develop that Power.” Paris: Chez Bachelier, Libraire, Quai Des Augustins, No. 55.
1. (a) Papin, Denis. (1690). “A New Way to Obtain Very Great Motive Powers at Small Cost” (Nova Methodus ad Vires Motrices Validissimas levi Pretio Comparandas). Acta Eruditorum, anno, Aug., pgs. 410-14.
(b) Muirhead, James. (1859). The Life of James Watt, (English translation: Ch. XI, Denys Pain: His memoir of 1690, Section: A New Way to Obtain Very Great Motive Powers at Small Cost”, pgs. 131-42). London: John Murray.
(c) The original Latin, accompanied by a translation, in Muirhead’s Mechanical Inventions of James Watt, Vol. III., pg. 139.