The Greek term energeia derives etymologically from en ("within") and ergein ("to work").
Thus energy is the actual or potential work that is immanent within a body.
Joule's principle of the conservation of energy is an example of the subsumption of qualitative transformations into a quantifiable entity. "Thus it is that order is maintained in the universe--nothing is deranged, nothing ever lost, but the entire machinery, complicated as it is, works smoothly and harmoniously." (Joule, quoted in Prigogine, p.108-9)
In the period from 1775-1825, the word and concept of energy was bruited about by all manners of literate individuals, often as a shorthand, or cipher for talking about organicism as a process uniting mind, nature, and art. (Stuart Peterfreund, "Organicism and the Birth of Energy" in Burwick, Approaches to Organic Form.)
Freud dynamic model of the unconscious, called "hydraulic" by critics, described energy flows that build up and seek release. In this model, tension is displeasure and will always seek an avenue for release.z