energy (n.) Look up energy at
1590s, "force of expression," from Middle French énergie (16c.), from Late Latin energia, from Greek energeia "activity, action, operation," from energos "active, working," from en "at" (see en- (2)) + ergon "work, that which is wrought; business; action" (see organ).

Used by Aristotle with a sense of "actuality, reality, existence" (opposed to "potential") but this was misunderstood in Late Latin and afterward as "force of expression," as the power which calls up realistic mental pictures. Broader meaning of "power" in English is first recorded 1660s. Scientific use is from 1807. Energy crisis first attested 1970.