In thermodynamics, energy (TR:1,984) (LH:59) (TL:2,043|#4), from en- meaning “in” + -ergon meaning “work”, from "erga" (NE:109) (Homer, 800BC), a term derived or related to Hera (NE:109), the supreme goddess of the Greek pantheon, the wife of the god Zeus (Egyptian equivalent: Amen-Ra), the supreme power; all being thematic to the Greek letter "Ε" (epsilon), meaning "sun"; the word coming into modern form in the works of Heraclitus (490BC), aka Hera-clitus, in the word “en-ergon” (εν-εργειας), meaning “in work” (or at work); later molded into the word "energia" (Aristotle, 300BC) meaning "to act"; defined as ½mv2 or kinetic energy of bodies (Young, 1807); taking its final modern form as the internal energy U of bodies or systems (Clausius, 1865).
In 2500BC, in Egyptian hieroglyph of a man with his arms raised, shown below, became, via Proto-Sinaitic and Phoenician cultural transmission, the root etymology of the Greek letter epsilon "E", symbolic of a person ‘in action’, or doing ‘work’ of some sort, i.e. expending ‘energy’ as we would say:
In 1,000BC, during the formation of the Greek alphabet, letter E became, as the letter epsilon (ε or Ε), the second vowel of the seven vowels, thematic to or named after the sun, the second planet in Greek cosmology.
In 800BC, Homer was using the term "erga" in the sense of "work".
In 490BC, Heraclitus, the “flux and fire” philosopher, was referring to en (εν) ergon (εργειας) as the father and king of all things, as follows:
- “En-ergon is the father of everything, king of all things and, out of it, all forms of contrast originate. Since ‘en-ergon’ is common to everything, it is vital for life itself.”
- — Heraclitus (490BC), Fragment #; cited by Gerrit Feekes (1986) in The Hierarchy of Energy Systems (pg. 1) 
Heraclitus, we note, also believed in the existence of the vacuum (or void), contrary to Parmenides, who considered the existence of a void or vacuum to be an anathema. This connects us with the Hooke principle (1675) of thermodynamics.
The isopsephy values, of en-ergon, are “55” (εν), which translates as: “one; with, within”, and “324” (εργειας), which renders as: “pure, sacred, holy”. Thus, en-ergon might crudely render, in secret word meaning, as "one who is with, at, or within work is pure, sacred, or holy", or something to this effect. This might render, accordingly, in what Csikszentmihalyi (1990) refers to as “flow”, meaning a state wherein one is so immersed in their “work”, that a sense of timelessness results.
In 350BC, Aristotle, building on Heraclitus, was using the term "energia", in the sense of "to act".
In 1769, Denis Diderot, in his discussion of how a thinking being can from from the elements employed the term "energy" as follows:
- “You can imagine that in the inert mass of the egg there is a hidden element which is waiting for the egg to develop in order to manifest its presence, or you can assume that this imperceptible element has insinuated itself into the egg through the shell at a time determined by the developmental process. But what is this element? Did it occupy space or not? How did it come or escape without moving? Where was it? What was it doing there or somewhere else? Was it created at the necessary moment? Was it already in existence waiting for a home? Was it the same stuff as this home or different? If it was the same, then it was material stuff. If it was different one cannot conceive of its inertia before the development of the egg or of its energy in the developed animal.“
In 1807, Thomas Young defined energy in the sense of what we now refer to as kinetic energy:
- “Since the height, to which a body will rise perpendicularly, is as the square of its velocity, it will preserve a tendency to rise to a height which is as the square of its velocity, whatever may be the path into which it is directed, provided that it meets which no abrupt angle. The same idea is somewhat more concisely expressed by the term energy, which indicates the tendency of a body to ascend or to penetrate to a certain distance, in opposition to a retarding force.”
- — Thomas Young (1807), “On Confined Motion”
The following is the most-cited definition of when thermodynamics historians tend to claim "energy" was officially introduced:
- The term energy may be applied, with great propriety, to the product of mass or weight of a body, into the square of the number expressing its velocity. Thus, if the weight of one ounce moves with a velocity of a foot in a second, we call its energy 1; if a second body of two ounces has a velocity of three feet in a second, its energy will be twice the square of three, or 18.”
- — Thomas Young (1807), “On Collisions”
Thermodynamics | Internal energy
In 1865, Rudolf Clausius, building on Heraclitus, Young, William Thomson, and many others, defined the "energy" (or internal energy) of a body, symbol U, which subsumed the concept of kinetic energy, thereby defining the energy of bodies or systems, generally, via of the first law of thermodynamics.
The following are related quotes:
- “The term energia was first used by Heraclitus to connote fire as the primary source of action. Heraclitus, in his Physics, considered energon the father of everything and the originator of all life on Gaia.”
- — Paris Arnopoulos (1993), Sociophysics: Cosmos and Chaos in Nature and Culture (pg. 21) 
- “The word ‘energy’ comes from the Latin energon, which is composed of en, which means “at”, and ergon, which means “work”. In the field of physics, work is described simply as the “transfer of energy from one system to another.”
- — Dick DeVos (1998), Rediscovering American Values (pg. 320) 
- Greek pantheon – Hmolpedia 2020.
- God character rescripts (subdomain) – Hmolpedia 2020.
- Thims, Libb. (2020). Human Chemical Thermodynamics — Chemical Thermodynamics Applied to the Humanities: Meaning, Morality, Purpose; Sociology, Economics, Ecology; History, Philosophy, Government, Anthropology, Politics, Business, Jurisprudence; Religion, Relationships, Warfare, and Love (§2: Alphabet) (pdf) (§36: Joule [§§36.1: | E = Sun (etymology)]). Publisher.
- Plutarch. (c.110), ‘De E apud Delphos’. Publisher.
- (a) Feekes, Gerrit B. (1986). The Hierarchy of Energy Systems: from Atom to Society (pg. 1). Pergamon Press.
(b) Lancaster, Justin. (1989). “The Theory of Radially Evolving Energy” (abs), International Journal of General Systems, 16: 43-73.
- Barry, Kieren. (1999). The Greek Qabalah: Alphabetic Mysticism and Numerology in the Ancient World (pdf) (#55, pg. 219; #324, pg. 229). Weiser.
- Flow – Hmolpedia 2020.
- Arnopoulos, Paris. (1993). Sociophysics: Cosmos and Chaos in Nature and Culture (pg. 21). Nova Publishers, 2005.
- DeVos, Dick. (1998). Rediscovering American Values (pg. 320). Penguin.
- Energy – Hmolpedia 2020.