Online Etymology Dictionary

endearing (adj.): 1660s, present participle adjective from endear. Related: Endearingly.
endearment (n.): "act of endearing," 1610s, from endear + -ment. Meaning "obligation of gratitude" is from 1620s; that of "action expressive of love" is from 1702.
endeavor (n.): early 15c., "pains taken to attain an object," literally "in duty," from phrase put (oneself) in dever "make it one's duty" (a partial translation of Old French mettre en deveir "put in duty"), from Old French dever "duty," from Latin debere "to owe" (see debt). One's endeavors meaning one's "utmost effort" is from late 15c.
endeavor (v.): c. 1400, from phrase put in dever (see endeavor (n.)). Related: Endeavored; endeavoring.
endeavour: chiefly British English spelling of endeavor (q.v.); for spelling, see -or. Related: Endeavoured; endeavoring; endeavours. The U.S. space shuttle was spelled this way because it was named for the HMS Endeavour, Capt. Cook's ship.
ended (adj.): "finished, completed," 1590s, past participle adjective from end (v.).
endemic (adj.): "particular to a people or locality," 1650s (endemical), with -ic + Greek endemos "native, dwelling in (a place), of or belonging to a people," from en "in" (see en- (2)) + demos "people, district" (see demotic). From 1660s as a noun.
endgame (n.): also end-game, 1850, in chess, from end + game (n.). There is no formal or exact definition of it in chess, but it begins when most of the pieces have been cleared from the board.
ending (n.): "a coming to an end," early 14c., verbal noun from end (v.). Meaning "the end part (of something)" is from c. 1400. Old English had endunge "ending, end, death."
endive (n.): late 14c., from Old French endive (14c.), from Medieval Latin endivia or a related Romanic source, from Latin intibus. This probably is connected in some way with Medieval Greek entybon, which Klein says is perhaps of Eastern origin (compare Egyptian tybi "January," the time the plant grows in Egypt). Century Dictionary says Arabic hindiba is "appar. of European origin."
endless (adj.): Old English endeleas "boundless, eternal;" see end (n.) + -less. Compare Old Saxon endilos, Dutch eindeloos, German endlos. Related: Endlessly; endlessness. Old English used endeleasnes for "infinity, eternity."
endlong (prep., adv.): c. 1200, "from end to end, lengthwise; through or over the length of," from Old English andlang "from end to end, lengthwise" (see along) with Middle English substitution of ende (see end (n.)) for first element. Meaning "at full length, horizontally" is from early 15c. In Middle English frequently paired with overthwart and together meaning "lengthwise and crosswise," hence "in all directions."
endmost (adj.): 1725, from end (n.) + -most. Middle English had endemest (adv.) "from end to end, throughout."
endo-: word-forming element meaning "inside, within, internal," comb. form of Greek endon "in, within," from PIE *en-do-, extended form of root *en "in" (see in (adv.)).
endocrine (adj.): "secreting internally," 1914, from endo- + Latinized form of Greek krinein "to separate, distinguish" (see crisis). Denoting glands having an internal secretion.
endocrinology (n.): 1917, from endocrine + -ology. Related: Endocrinologist.
endoderm (n.): 1835, from endo- + -derm. Coined by Prussian embryologist Robert Remak (1815-1865).
endogamy (n.): "marriage within the tribe or group," 1865, from endo- on model of polygamy. Related: Endogamous (1865). Opposed to exogamy. Apparently both were coined by Scottish anthropologist John Ferguson McLennan (1827-1881) in "Primitive Marriage."
To this law, the converse of caste, forbidding marriage within the tribe, Mr. M'Lennan has given the name of exogamy: while, instead of caste, since that word involves notions unconnected with marriage, he has used the correlative word -- endogamy. [review in "The Lancet," March 25, 1865]
endogenous (adj.): "growing or proceeding from within," especially with reference to a class of plants including cereals, palms, plantains, etc., 1822, from endo- "within" + -genous "producing."
endometrium (n.): "lining membrane of the uterus," 1882, medical Latin, from endo- + Greek metra "uterus," related to meter (see mother (n.1)). Related: Endometrial (1870).
endomorph (n.): 1940 as one of W.H. Sheldon's three types of human bodies, from endo- + -morph, from Greek morphe "form" (see Morpheus). Earlier, "a mineral encased in the crystal of another mineral" (1874). Related: Endomorphic.
endorphin (n.): "chemical which occurs naturally in the brain and works like morphine," 1975, from French endorphine. First element from endogène "endogenous, growing within" (see endo- + genus); second element from morphine.
endorse (v.): c. 1400, endosse "confirm or approve" (a charter, bill, etc.), originally by signing or writing on the back of the document, from Old French endosser (12c.), literally "to put on the back," from en- "put on" (see en- (1)) + dos "back," from Latin dossum, variant of dorsum "back" (see dorsal). Assimilated 16c. in form to Medieval Latin indorsare. Figurative sense of "confirm, approve" is recorded in English first in 1847. Related: Endorsed; endorsing.
You can endorse, literally, a cheque or other papers, &, metaphorically, a claim or argument, but to talk of endorsing material things other than papers is a solecism. [Fowler]
endorsement (n.): 1540s, from endorse + -ment. Figurative use from 1630s. Earlier endosement (early 15c.).
endoscopy (n.): 1861, from endo- + -scopy.
endoskeleton (n.): 1838, from endo- + skeleton.
endosperm (n.): 1819, perhaps from German, from endo- + sperm.
endospore (n.): 1859, perhaps from French, from endo- + spore.
endothermic (adj.): 1866, from French endothermique; see endo- + thermal.
endow (v.): late 14c., indowen "provide an income for," from Anglo-French endover, from en- "in" (see en- (1)) + Old French douer "endow," from Latin dotare "bestow" (see dowry). Related: Endowed; endowing.
endowed (adj.): 1700, past participle adjective from endow.
endowment (n.): mid-15c., "action of endowing," from endow + -ment. Meaning "property with which an institution or person is endowed" is from 1590s; that of "gift, power, advantage" is early 17c.
endpoint (n.): also end-point, 1844, originally in geometry, later chemistry; from end (n.) + point (n.). General use by 1920s.
endue (v.): also indue, c. 1400, "invest (with) some gift, quality, or power" (usually passive), from Old French enduire, induire "lead, drive, initiate, indoctrinate" (12c.) and directly from Latin inducere "to lead" (see induce). Related: Endued.
endurable (adj.): c. 1600, "able to endure," from endure + -able, or from French endurable. Meaning "able to be endured" is from 1744. Related: Endurably.
endurance (n.): late 15c., "continued existence in time;" see endure + -ance. Meaning "ability to bear suffering, etc." is from 1660s.
endure (v.): late 14c., "to undergo or suffer" (especially without breaking); also "to continue in existence," from Old French endurer (12c.) "make hard, harden; bear, tolerate; keep up, maintain," from Latin indurare "make hard," in Late Latin "harden (the heart) against," from in- (see in- (2)) + durare "to harden," from durus "hard," from PIE *dru-ro-, from root *deru- "be firm, solid, steadfast" (see true).

Replaced the important Old English verb dreogan (past tense dreag, past participle drogen), which survives in dialectal dree. Related: Endured; endures.
enduring (adj.): "lasting," 1530s, present participle adjective from endure.
Endymion: beautiful youth, son of Jupiter and Calyce, beloved by Moon-goddess Selene, from Greek, perhaps literally "diver, plunger," from endyein "to enter into, sink into, plunge, dive," which was used in reference to the sun or stars setting into the sea. On this theory, he originally was a solar deity, a personification of the setting sun.
enema (n.): early 15c., via Medieval Latin, from Greek enema "injection," from enienai "to send in, inject," from en "in" (see en- (2)) + hienai "send" (cognate of Latin iacere; see jet (v.)).
enemy (n.): early 13c., "one hateful toward and intent on harming (someone)," from Old French enemi (12c., Modern French ennemi), earlier inimi (9c.) "enemy, adversary, foe; demon, the Devil," from Latin inimicus "an enemy," literally "an unfriend," noun use of adjective meaning "hostile, unfriendly" (source also of Italian nemico, Catalan enamic, Spanish enemigo, Portuguese inimigo), from in- "not" (see in- (1)) + amicus "friend" related to amare "to love" (see Amy). From c. 1300 in English as "adversary of God, unbeliever, heathen, anti-Christian;" late 14c. as "the Devil;" also late 14c. as "member of an armed, hostile body in a war, feud, etc.;" of the opposing military forces as a whole, from c. 1600. From mid-14c. as an adjective.

Most Indo-European words for "personal enemy" cover also "enemy in war," but certain languages have special terms for the latter, such as Greek polemioi (distinct from ekhthroi), Latin hostis, originally "stranger" (distinct from inimicus), Russian neprijatel' (distinct from vrag). Russian vrag (Old Church Slavonic vragu) is cognate with Lithuanian vargas "misery" (see urge (v.)), and probably is related to Proto-Germanic *wargoz, source of Old Norse vargr "outlaw," hence "wolf;" Icelandic vargur "fox;" Old English wearg "criminal, felon;" which likely were the inspirations for J.R.R. Tolkien's warg as the name of a kind of large ferocious wolf in "The Hobbit" (1937) and "Lord of the Rings." Related: Enemies.
energetic (adj.): 1650s, "powerful in operation," from Greek energetikos "active," from energein "to work, be in action, act upon" (see energy). Of persons, "active," in English from 1796 (energetical "operative" is from c. 1600; from 1630s as "full of energy," while energical is attested from 1560s). Related: Energetically.
energize (v.): 1751; see energy + -ize. Related: Energized; energizing.
energizer (n.): 1750, agent noun from energize.
energy (n.): 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.
enervate (v.): c. 1600, "deprive of force or strength," from Latin enervatus, past participle of enervare "to weaken" (see enervation). Literal sense of "to weaken, impair" in English is from 1610s. Related: Ennervated; ennervating. As a verb Middle English had enerve (c. 1400, eneruyd).
enervation (n.): early 15c., "impairment, infringement," from Middle French énervation, from Late Latin enervationem (nominative enervatio), noun of action from past participle stem of Latin enervare "weaken," literally "cut the sinews of," from ex- "out" (see ex-) + nervus "sinew" (see nerve (n.)). Figurative sense is from 1550s.
enfant terrible (n.): 1851, French, literally "terrible child" (see infant + terrible). One whose unorthodox or shocking speech or manners embarrass his associates as a naughty child embarrasses his elders. French also has enfant gâté, "spoiled child," hence "person given excessive adulation."
enfeeble (v.): "to cause to weaken, deprive of strength," mid-14c., from Old French enfeblir "become weak," from en- (see en- (1)) + feble (see feeble). Related: Enfeebled; enfeebling; enfeeblement.
enfeoff (v.): c. 1400, based on Old French enfeffer, from en- "in" (see en- (1)) + feoff, variant of fief (n.). Related: Enfeoffment.