Online Etymology Dictionary

eidolon (n.): 1801, "a shade, a specter," from Greek eidolon "appearance, reflection in water or a mirror," later "mental image, apparition, phantom," also "material image, statue, image of a god, idol," from eidos "form, shape" (see -oid). By 1881 in English as "a likeness, an image."
Eiffel Tower: erected in the Champ-de-Mars for the Paris Universal Exposition of 1889; at 984.25 feet the world's tallest structure at the time. Designed by French engineer Alexandre Gustave Eiffel (1832-1923).
eight (n.): late 14c., eighte, earlier ehte (c. 1200), from Old English eahta, æhta, from Proto-Germanic *akhto (source also of Old Saxon ahto, Old Frisian ahta, Old Norse atta, Swedish åtta, Dutch acht, Old High German Ahto, German acht, Gothic ahtau), from PIE *okto(u) "eight" (source also of Sanskrit astau, Avestan ashta, Greek okto, Latin octo, Old Irish ocht-n, Breton eiz, Old Church Slavonic osmi, Lithuanian aštuoni). From the Latin word come Italian otto, Spanish ocho, Old French oit, Modern French huit.

For spelling, see fight (v.). Meaning "eight-man crew of a rowing boat" is from 1847. The Spanish piece of eight (1690s) was so called because it was worth eight reals (see piece (n.)). Figure (of) eight as the shape of a race course, etc., attested from c. 1600. To be behind the eight ball "in trouble" (1932) is a metaphor from shooting pool. Eight hours as the ideal length of a fair working day is recorded by 1845.
eighteen (n.): late 14c., eightene, earlier ahtene (c. 1200), from Old English eahtatiene, eahtatyne; see eight + -teen. Cognate with Old Frisian schtatine, Old Saxon ahtotian, Dutch achttien, Old High German ahtozehan, German achtzehn, Old Norse attjan, Swedish adertån.
eighteenth (adj.): mid-13c., egtetenþe, modified, by influence of eighteen, from Old English eahtateoða; from eight + teoða "tenth" (see -ty (1)). Cognate with German achtzehnte, Danish attende, Swedish adertonde.
eightfold (adj.): Old English eahtafeald; see eight + -fold.
eighth: late 14c., eighthe, contracted from Old English eahtoða; see eight + -th (1). Cognate with Old High German ahtoda, Old Frisian achta, German achte, Gothic ahtuda.
eighties (n.): 1827 as the years of someone's life between ages 80 and 89; from 1833 as the ninth decade of years in a given century; from 1854 with reference to Fahrenheit temperature. See eighty.
eighty (n.): eigteti (late 13c.), from eight + -ty (1). Replacing Old English hundeahtatig, with hund- "ten." Related: Eightieth.
eighty-six (v.): slang for "eliminate," 1936, originated at lunch counters, a cook's word for "none" when asked for something not available, probably rhyming slang for nix.
Eileen: fem. proper name, from Celtic (compare Irish Eibhlin) but influenced in form by Helen.
Einstein (n.): as a type-name for a person of genius, 1920, in reference to German-born theoretical physicist Albert Einstein (1879-1955), who was world-famous from 1919 through media accounts of his work in theoretical physics. According to "German-American Names" (George F. Jones, 3rd ed., 2006) it means literally "place encompassed by a stone wall."
einsteinium (n.): radioactive element, discovered in the debris of a 1952 U.S. nuclear test in the Pacific, named 1955 for physicist Albert Einstein (1879-1955). With metallic element ending -ium.
Eire: ultimately from Old Irish Eriu (accusative Eirinn, Erinn). The reconstructed ancestry of this derives it from Old Celtic *Iveriu (accusative *Iverionem, ablative *Iverione), perhaps (Watkins) from PIE *pi-wer- "fertile," literally "fat," from root *peie- "to be fat, swell" (see fat (adj.)).
eirenic (adj.): "tending toward or productive of peace," 1866, from Greek eirenikos, from eirene "peace, time of peace." Earlier as irenic (1864), irenical (1650s).
eisegesis (n.): the reading of one's own ideas into scripture, 1859, from Greek eis "in, into" + ending from exegesis. Related: Eisegetical.
Eisenhower: surname, from German Eisenhauer, literally "iron-cutter, iron-hewer," "perhaps based on Fr. Taillefer" [George F. Jones, "German-American Names," 3rd ed., 2006]. See iron (n.) + hew (v.).
Eisteddfod (n.): "annual assembly of Welsh bards," 1822, from Welsh eisteddfod "congress of bards or literati," literally "a session, a sitting," from eistedd "to sit" (from sedd "seat," cognate with Latin sedere; see sedentary) + bod "to be" (cognate with Old English beon; see be). The Welsh plural is eisteddfodau.
either: Old English ægðer, contraction of æghwæðer (pron., adv., conj.) "each of two, both," from a "always" (see aye (adv.)) + ge- collective prefix + hwæðer "which of two, whether" (see whether). Cognate with Dutch ieder, Old High German eogiwedar, German jeder "either, each, every").

Modern sense of "one or the other of two" is late 13c. Adverbially, for emphasis, "in any case, at all," especially when expressing negation, by 1828. Use of either-or to suggest an unavoidable choice between alternatives (1931) in some cases reflects Danish enten-eller, title of an 1843 book by Kierkegaard.
ejaculate (v.): 1570s, "emit semen," from Latin eiaculatus, past participle of eiaculari "to throw out, shoot out," from ex- "out" (see ex-) + iaculari "to throw, hurl, cast, dart," from iaculum "javelin, dart," from iacere "to throw" (see jet (v.)). Sense of "exclaim suddenly" is from 1660s. Related: Ejaculated; ejaculating; ejaculatory.
ejaculation (n.): c. 1600, of fluids; 1620s, of utterances, from French éjaculation, noun of action from éjaculer, from Latin ejaculari (see ejaculate).
eject (v.): mid-15c., from Latin eiectus "thrown out," past participle of eicere "throw out, cast out, thrust out; drive into exile, expel, drive away," from ex- "out" (see ex-) + -icere, comb. form of iacere "to throw" (see jet (v.)). Related: Ejected; ejecting. Ejecta "matter thrown out by a volcano" is from 1851.
ejection (n.): 1560s, from Middle French ejection and directly from Latin eiectionem (nominative eiectio) "a casting out, banishment, exile," noun of action from past participle stem of eicere (see eject). The jet pilot's ejection seat (also ejector seat) is from 1945.
eke (v.): c. 1200, eken "to increase, lengthen," north England and East Midlands variant of echen from Old English ecan, eacan, eacian "to increase," probably from eaca "an increase," from Proto-Germanic *aukan (source also of Old Norse auka, Danish öge, Old Frisian aka, Old Saxon okian, Old High German ouhhon, Gothic aukan), from PIE *aug- (1) "to increase" (see augment). Now mainly in phrase to eke out (1590s), wherein it means "to make a supply of something go further or last longer." Related: Eked; eking.
eke (adv.): "also" (obsolete), from Old English eac, cognate with Old Saxon, Old Dutch ok, Old Norse and Gothic auk, Old Frisian ak, Old High German ouh, German auch "also;" probably related to eke (v.).
el (n.): American English abbreviation of elevated railroad, first recorded 1906 in O. Henry. See L.
el: Spanish article, from Latin ille "that."
El Paso: city in Texas, named for the nearby pass where the Rio Grande emerges from the Rockies, Spanish, short for el paso del norte "the northern pass;" see pass (n.1).
elaborate (adj.): 1590s, "wrought by labor," from Latin elaboratus, past participle of elaborare "to exert oneself" (see elaboration). Meaning "very detailed" is from 1620s, via notion of "produced with great care and attention to detail." Related: elaborateness.
elaborate (v.): c. 1600, "to build up from simple elements," from Latin elaboratus, past participle of elaborare "to labor, endeavor, struggle, work out" (see elaboration). Meaning "to work out in detail" is attested from 1610s. Related: Elaborated; elaborating.
elaborately (adv.): 1630s, "with attention to exactness;" see elaborate (adj.) + -ly (2).
elaboration (n.): 1570s, in a physiological sense relating to tissue development, from Late Latin elaborationem (nominative elaboratio), noun of action from past participle stem of Latin elaborare "work out, produce by labor, endeavor, struggle," from ex- "out" (see ex-) + laborare "to labor" (see labor (v.)). Meaning "act of working out in great exactness and detail" is from 1610s.
elan (n.): "vivacity," 1877, from French élan (16c.), "spring, bound, impetus," noun derived from élancer "to shoot, incite" (trans.); "rush forward, dart" (intrans.), from Old French elancer, from e- "out" (see ex-) + lancer "to throw," originally "to throw a lance," from Late Latin lanceare, from Latin lancea (see lance (n.)).
eland (n.): Cape elk, large South African antelope, 1786, from Dutch eland "elk," probably from a Baltic source akin to Lithuanian elnias "deer," from PIE *el- (2) "red, brown" (see elk), cognate with first element in Greek Elaphebolion, name of the ninth month of the Attic year (corresponding to late March-early April), literally "deer-hunting (month)." Borrowed earlier in English as ellan (1610s, via French), ellend (from the German form of the word).
elapse (v.): 1640s, from Middle French elapser, from Latin elapsus, past participle of elabi "slip or glide away, escape," from ex- "out, away" (see ex-) + labi "to slip, glide" (see lapse (n.)). The noun now corresponding to elapse is lapse, but elapse (n.) was in recent use. Related: Elapsed; elapsing.
elasmobranch (n.): 1859, from Elasmobranchii, class of fishes that includes sharks and rays, from comb. form of Greek elasmos "metal plate," from elan "to strike" (see elastic) + brankhia "gill."
elasmosaurus (n.): giant sea reptile from the Mezozoic, 1868, from Modern Latin (coined by E.D. Cope), from comb. form of Greek elasmos "metal plate" (from elan "to strike;" see elastic) + -saurus. So called from the caudal laminae and the great plate-bones.
elastic (adj.): 1650s, formerly also elastick, coined in French (1650s) as a scientific term to describe gases, from Modern Latin elasticus, from Greek elastos "ductile, flexible," related to elaunein "to strike, beat out," which is of uncertain origin; according to Watkins from an extended form of the PIE base *ele- "to go." Applied to solids from 1670s. Figurative use by 1859. The noun meaning "piece of elastic material," originally a cord or string woven with rubber, is from 1847, American English.
elasticity (n.): 1660s, from French élasticité, or else from elastic + -ity.
elate (v.): 1570s, literal, "to raise, elevate," probably from Latin elatus "uplifted, exalted," past participle of effere "carry out, bring forth" (see elation), or else a back-formation from elation. Figurative use, "to raise or swell the mind or spirit with satisfaction and pride," is from 1610s. Related: Elated; elating.
elated (adj.): 1610s, past participle adjective from elate.
elation (n.): late 14c., "inordinate self-esteem, arrogance," especially "self-satisfaction over one's accomplishments or qualities, vainglory" (early 15c.), from Old French elacion "elation, conceit, arrogance, vanity," from Latin elationem (nominative elatio) "a carrying out, a lifting up," noun of action from elatus "elevated," form used as past participle of efferre "carry out, bring out, bring forth, take away," from assimilated form of ex- "out" (see ex-) + latus (see oblate (n.)), past participle of ferre "carry" (see infer). Metaphoric sense of "a lifting of spirits" was in Latin and has always been the principal meaning in English. More positive sense of "buoyancy, joyfulness" is from 1750 in English.
elbow (n.): "bend of the arm," c. 1200, elbowe, from a contraction of Old English elnboga "elbow," from Proto-Germanic *elino-bugon, literally "bend of the forearm" (source also of Middle Dutch ellenboghe, Dutch elleboog, Old High German elinbogo, German Ellenboge, Old Norse ölnbogi). For first element, see ell (n.1) "length of the forearm;" second element represented by Old English boga "bow, arch" (see bow (n.1)).

Second element related to Old English bugan "to bend" (see bow (v.)); first element from *alina "arm," from PIE *el- (1) "elbow, forearm" (see ell (n.1)). To be out at elbows (1620s) was literally to have holes in one's coat. Phrase elbow grease "hard rubbing" is attested from 1670s, from jocular sense of "the best substance for polishing furniture." Elbow-room, "room to extend one's elbows," hence, "ample room for activity," attested 1530s.
elbow (v.): "thrust with the elbow," c. 1600, from elbow (n.). Figurative sense is from 1863. Related: Elbowed; elbowing.
eld (n.): "former ages, old times," c. 1400, poetic or archaic form of old; in some cases from Old English eald, yldu, yldo "old age, an age, age as a period of life."
elder (adj.): "more old," Old English (Mercian) eldra, comparative of eald, ald (see old); only English survival of umlaut in comparison. Superseded by older since 16c. Elder statesman (1921) originally was a translation of Japanese genro (plural).
elder (n.2): type of berry tree, c. 1400, with excrescent -d- from earlier ellen, from Old English ellæn, ellærn "elderberry tree," origin unknown, perhaps related to alder, which at any rate might be the source of the -d-. Common Germanic, cognates: Old Saxon elora, Middle Low German elre, Old High German elira, German Eller, Erle. Related: Elderberry.
elder (n.1): "elderly person, senior citizen," c. 1200, from Old English eldra "older person, parent; ancestor; chief, prince" (used in biblical translation for Greek presbyter); see elder (adj.). Compare German Eltern, Danish forældre, Swedish föräldrar "parents." The Old English for "grandfather" was ealdfæder.
elderly (adj.): "bordering on old age, somewhat old," 1610s, from elder + -ly (1). Now, generally, "old." Old English ealdorlic meant "chief, princely, excellent, authentic." Old English also had related eldernliche "of old time," literally "forefatherly."
eldest (adj.): Old English (Mercian) eldrost "most advanced in age, that was born first," superlative of eald, ald "old" (see old). Superseded by oldest since 16c. Compare elder (adj.).