1590s, "force of expression," from French énergie (16c.), from Late Latin energia, from Greek energeia "activity, action, operation," from energos "active, working," from en "at" (see en- (2)) + -ergos "that works," from ergon "work, that which is wrought; business; action" (from PIE root *werg- "to do").
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.
late 14c., "power, efficacy," from Medieval Latin actualitatem (nominative actualitas), from Late Latin actualis "pertaining to action," from Latin actus "a doing" (from PIE root *ag- "to drive, draw out or forth, move"). A Latin loan-translation of Greek energeia "activity, action, operation" (see energy). Meaning "state of being real" is from 1670s (actualities "existing conditions" is from 1660s).
Mod. use of actuality in the sense of realism, contact with the contemporary, is due to Fr. actualité, from actuel, which does not mean actual, real, but now existing, up to date. [Weekley]
It forms all or part of: allergic; allergy; argon; boulevard; bulwark; cholinergic; demiurge; dramaturge; energy; erg (n.1) "unit of energy;" ergative; ergonomics; ergophobia; George; georgic; handiwork; irk; lethargic; lethargy; liturgy; metallurgy; organ; organelle; organic; organism; organize; orgy; surgeon; surgery; synergism; synergy; thaumaturge; work; wright; wrought; zymurgy.
It is the hypothetical source of/evidence for its existence is provided by: Greek ergon "work," orgia "religious performances;" Armenian gorc "work;" Avestan vareza "work, activity;" Gothic waurkjan, Old English wyrcan "to work," Old English weorc "deed, action, something done;" Old Norse yrka "work, take effect."
"vigor, energy," 1912, shortened form of pepper (n.), which was used in the figurative sense of "spirit, energy" from at least 1847. Pep rally "meeting to inspire enthusiasm" is attested from 1915; pep talk is from 1926. To pep (something) up "fill or inspire with vigor or energy" is from 1925.
"paralyzed; deprived of energy or power of action," 1540s, past-participle adjective from palsy.
"pertaining to the radiometer or to experiments performed by it," 1877, from radiometer "instrument to transform radiant energy into mechanical work" (1875), radiometry, from radio-, here indicating "radiant energy," + -metric. Previously radiometer was the name of an old cross-staff instrument for measuring angles. Radiometric dating is attested from 1906.