Achilles
Greek hero of the Trojan War stories, son of Thetis and Peleus, his name is perhaps a compound of akhos "pain, grief" (see awe) + laos "the people, a people" (see lay (adj.)); or else it is from a pre-Greek language.
Achilles tendon
from Modern Latin tendo Achillis, first used by German surgeon Heister and so-called in reference to the one vulnerable spot of the great Greek hero Achilles, whose mother held him by the heel when she dipped him in the River Styx to render him invulnerable (though this story is not in Homer and not found before 1c. C.E.). Earlier Achilles' sinew, from Modern Latin chorda Achillis, coined 1693 by Dutch anatomist Philip Verheyden when dissecting his own amputated leg. Hence figurative use of heel of Achillies for "vulnerable spot" (1810).
achromatic (adj.)
1766, from Greek akhromatos "colorless," from a-, privative prefix (see a- (3)), + khromat-, comb. form of khroma "color" (see chroma) + -ic.
achtung
German word used to command attention, from German achtung, from acht (n.) "attention, care, heed, consideration," achten (v.) "pay attention to, regard, esteem, respect," from Old High German ahton "pay attention to," a general Germanic word akin to Old English eahtian "to estimate, esteem, consider, praise," but with no living native descendants in English.
achy (adj.)
1875, first recorded in George Eliot's letters, from ache + -y (2). Middle English had akeful "painful" (early 15c.). Related: Achily; achiness.
acid (adj.)
1620s, "of the taste of vinegar," from French acide (16c.) or directly from Latin acidus "sour, sharp," adjective of state from acere "to be sour," from PIE root *ak- "sharp, pointed" (see acrid). Figurative use from 1775; applied to intense colors from 1916. Acid test is American English, 1892, from the frontier days, when gold was distinguished from similar metals by application of nitric acid. Acid rain is first recorded 1859 in reference to England.
acid (n.)
1690s, from acid (adj.). Slang meaning "LSD-25" first recorded 1966 (see LSD).
When I was on acid I would see things that looked like beams of light, and I would hear things that sounded an awful lot like car horns. [Mitch Hedberg, 1968-2005, U.S. stand-up comic]
Acid rock (type played by or listen to by people using LSD) is also from 1966; acid house dance music style is 1988, probably from acid in the hallucinogenic sense + house "dance club DJ music style."
acidic (adj.)
1877, originally in geology; see acid (n.) + -ic.
acidity (n.)
1610s, from French acidité (26c.) or directly from Latin aciditatem (nominative aciditas), noun of quality from Latin acidus (see acid (adj.)).
acidophilus (adj.)
1920, used of milk fermented by acidophilic bacteria, from acidophil (1900), a hybrid word, from Latin acidus "acidic" (see acid (adj.)) + Greek philos "loving" (see -phile); the bacteria so called because they stain easily with an acid dye.
acidulous (adj.)
1769, "sub-acidic," used figuratively for "sour-tempered;" from Latin acidulus "slightly sour," a diminutive of acidus (see acid (adj.)).
ack
British oral code for letter A in wireless and telephone communication, 1898; hence ack-ack "anti-aircraft" (gun, fire, etc.).
ack-ack
1939, representing A.A., the military abbreviation for anti-aircraft (see ack).
acknowledge (v.)
1550s, a blend of Middle English aknow (from Old English oncnawan "understand," from on + cnawan "recognize;" see know) and Middle English knowlechen "admit, acknowledge" (c.1200; see knowledge). In the merger, a parasitic -c- slipped in, so that while the kn- became a simple "n" sound (as in know), the -c- stepped up to preserve, in this word, the ancient "kn-" sound. Related: Acknowledged; acknowledging.
acknowledgement (n.)
1590s, "act of acknowledging," from acknowledge + -ment. "An early instance of -ment added to an orig. Eng. vb." [OED]. Meaning "token of due recognition" is recorded from 1610s.
acknowledgment (n.)
alternative form of acknowledgement. OED deems it "a spelling more in accordance with Eng. values of letters."
acme (n.)
"highest point," 1560s, from Greek akme "(highest) point, edge; peak of anything," from PIE root *ak- "sharp" (see acrid). Written in Greek letters until c.1620. The U.S. grocery store chain was founded 1891 in Philadelphia, Pennsylvania.
acne (n.)
1813, from Modern Latin, from aknas, a 6c. Latin clerical misreading of Greek akmas, accusative plural of akme "point" (see acme). The "pointed" pimples are the source of the medical use.
acolyte (n.)
early 14c., "inferior officer in the church," from Old French acolite or directly from Medieval Latin acolytus (Late Latin acoluthos), from Greek akolouthos "following, attending on," literally "having one way," from a- "together with," copulative prefix, + keleuthose "a way, road, path, track," from PIE *qeleu- (cognates: Lithuanian kelias "way"). In late Old English as a Latin word.
acomia (n.)
"baldness," Modern Latin, from Greek akomos "hairless," from a-, privative prefix (see a- (3)) + kome "hair" (see comet).
aconite (n.)
poisonous plant (also known as monkshood and wolf's bane), 1570s, from French aconit, from Latin aconitum, from Greek akoniton, of unknown origin.
acorn (n.)
Old English æcern "nut," common Germanic (cognates: Old Norse akarn, Dutch aker, Low German ecker "acorn," German Ecker, Gothic akran "fruit"), originally the mast of any forest tree, and ultimately related (via notion of "fruit of the open or unenclosed land") to Old English æcer "open land," Gothic akrs "field," Old French aigrun "fruits and vegetables" (from a Germanic source); see acre.

The sense gradually restricted in Low German, Scandinavian, and English to the most important of the forest produce for feeding swine, the mast of the oak tree. Spelling changed 15c.-16c. by folk etymology association with oak (Old English ac) and corn (n.1).
acoustic (adj.)
c.1600, from French acoustique, from Greek akoustikos "pertaining to hearing," from akoustos "heard, audible," verbal adjective from akouein "to hear," probably from copulative prefix a- + koein "to mark, perceive, hear," from PIE *kous- "to hear," perhaps from root *(s)keu- "to notice, observe" (see caveat). Acoustic guitar (as opposed to electric) attested by 1958. Related: Acoustical; acoustically.
acoustics (n.)
1680s, "science of sound," from acoustic (also see -ics). Meaning "acoustic properties" of a building, etc., attested from 1885.
acquaint (v.)
early 13c., from Old French acointier "make known, make acquaintance of," from Vulgar Latin accognitare "to make known," from Latin accognitus "acquainted with," past participle of accognoscere "know well," from ad- "to" (see ad-) + cognitus, past participle of cogniscere "come to know," from com- "with" (see com-) + gnoscere "know" (see notice). Originally reflexive, "to make oneself known;" sense of "to gain for oneself personal knowledge of" is from early 14c. Related: Acquainted; acquainting.
acquaintance (n.)
c.1300, "state of being acquainted;" late 14c., "person with whom one is acquainted;" also "personal knowledge;" from Old French acointance "acquaintance, friendship, familiarity," noun of action from acointer (see acquaint). Acquaintant (17c.), would have been better in the "person known" sense but is now obsolete.
acquainted (adj.)
early 13c., "personally known;" past participle adjective from acquaint (v.). Of skills, situations, etc., from late 15c.
I have been one acquainted with the night.
I have walked out in rain —- and back in rain.
I have outwalked the furthest city light.

[Robert Frost, from "Acquainted with the Night"]
acquiesce (v.)
1610s, from Middle French acquiescer (16c.), from Latin acquiescere "to become quiet, remain at rest," thus "be satisfied with," from ad- "to" (see ad-) + quiescere "to become quiet," from quies (genitive quietis) "rest, quiet" (see quiet (n.)). Related: Acquiesced; acquiescing.
acquiescence (n.)
1630s, "act of acquiescing," from French acquiescence, noun of action from acquiescer (see acquiesce). Meaning "silent consent" is recorded from 1640s.
acquiescent (adj.)
1690s (implied in acquiescently), from Latin acquiescentem (nominative acquiescens), present participle of acquiescere (see acquiesce).
acquire (v.)
mid-15c., acqueren, from Old French aquerre "acquire, gain, earn, procure," from Vulgar Latin *acquaerere, from Latin acquirere "to seek in addition to" (see acquisition). Reborrowed in current form from Latin c.1600. Related: Acquired; acquiring.
acquired (adj.)
c.1600, "gained by effort," past participle adjective from acquire. Of diseases, "occurring after birth, thus not dependent on heredity," 1842 (opposed to congenital). Acquired taste is attested from 1734.
acquisition (n.)
late 14c., "act of obtaining," from Old French acquisicion (13c.) or directly from Latin acquisitionem (nominative acquisitio), noun of action from past participle stem of acquirere "get in addition, accumulate," from ad- "extra" (see ad-) + quaerere "to seek to obtain" (see query (v.)). Meaning "thing obtained" is from late 15c. The vowel change of -ae- to -i- in Latin is due to a Latin phonetic rule involving unaccented syllables in compounds.
acquisitive (adj.)
1630s, "owned through acquisition," from Latin acquisit-, past participle stem of acquirere (see acquisition) + -ive. Meaning "given to acquisition, avaricious" is from 1826 (implied in acquisitiveness). Related: Acquisitively (1590s).
acquit (v.)
early 13c., "to satisfy a debt" (either for oneself or on behalf of another), from Old French aquiter "pay, pay up, settle a claim" (12c.), from à "to" (see ad-) + quite "free, clear" (see quit (adj.)). Meanings "set free from charges" and "to discharge one's duty" both recorded from late 14c. Related: Acquitted; acquitting.
acquittal (n.)
early 15c., "payment of debt or retribution;" see acquit + -al (2). Sense of "a release from debt or obligation" is from mid-15c.; that of "freeing from charge or offense" (by legal process) is from 1530s.
acquitted (adj.)
"freed, exonerated," 1670s, past participle adjective from acquit (v.). Formerly in this sense was acquit (late 14c.), perhaps on analogy of pps. such as hit.
acre (n.)
Old English æcer "tilled field, open land," from Proto-Germanic *akraz "field, pasture" (cognates: Old Norse akr, Old Saxon akkar, Old Frisian ekker, Middle Dutch acker, Dutch akker, Old High German achar, German acker, Gothic akrs), from PIE *agro- "field" (cognates: Latin ager "field, land," Greek agros, Sanskrit ajras "plain, open country").

Originally in English without reference to dimension; in late Old English the amount of land a yoke of oxen could plow in a day, afterward defined by statute as a piece 40 poles by 4, or an equivalent shape (5 Edw. I, 31 Edw. III, 24 Hen. VIII). Original sense retained in God's acre "churchyard."
acrid (adj.)
1712, formed irregularly from Latin acer (fem. acris) "sharp, pungent, bitter, eager, fierce," from PIE *akri- "sharp," from root *ak- "be sharp, rise (out) to a point, pierce" (cognates: Oscan akrid (ablative singular) "sharply;" Greek akis "sharp point," akros "at the farthest point, highest, outermost," akantha "thorn," akme "summit, edge;" also oxys "sharp, bitter;" Sanskrit acri- "corner, edge," acani- "point of an arrow," asrih "edge;" Lithuanian ašmuo "sharpness," akstis "sharp stick;" Old Lithuanian aštras, Lithuanian aštrus "sharp;" Old Church Slavonic ostru, Russian óstryj "sharp;" Old Irish er "high;" Welsh ochr "edge, corner, border;" Old Norse eggja "goad;" Old English ecg "sword"). The -id suffix probably is in imitation of acid. Acrious (1670s) is a correct formation, but seldom seen.
acrimonious (adj.)
1610s, "acrid," from French acrimonieux, from Medieval Latin acrimoniosus, from Latin acrimonia (see acrimony). Of dispositions, debates, etc., from 1775. Related: Acrimoniously; acrimoniousness.
acrimony (n.)
1540s, "quality of being acrid," from Middle French acrimonie or directly from Latin acrimonia "sharpness, pungency of taste," figuratively "acrimony, severity, energy," from acer "sharp" (fem. acris, neuter acre; see acrid) + -monia suffix of action, state, condition. Figurative extension to "sharpness of temper" is first recorded 1610s.
acro-
word-forming element meaning "highest, topmost, at the extremities," before vowels, acr-, from Greek akro- "pertaining to an end, extreme," comb. form of akros "at the end, at the top" (see acrid).
acrobat (n.)
1825, from French acrobate (14c.), "tightrope-walker," and directly from Greek akrobates "rope dancer, gymnastic performer," related to akrobatos "going on tip-toe, climbing up high," from akros "topmost, at the point end" (see acrid) + stem of bainein "walk, go" (see come).
acrobatic (adj.)
1848; see acrobat + -ic. Related: Acrobatically.
acrobatics (n.)
1859, from acrobatic; also see -ics. Also acrobatism (1864). In early 20c. acrobacy (from French acrobacie) sometimes was used.
acromegaly (n.)
"gigantism due to activity of pituitary after normal growth has ceased," 1886, from French acromégalie, from medical Latin acromegalia, from Greek akron "extremity" (see acrid) + megas "great" (fem. megale; see mickle). Said in contemporary literature to have been coined 1885 by French physician Dr. Pierre Marie.
acronym (n.)
word formed from the first letters of a series of words, 1943, American English coinage from acro- + -onym "name" (abstracted from homonym; see name (n.)). But for cabalistic esoterica and acrostic poetry, the practice was practically non-existent before 20c. For distinction of usage, see initialism.
acrophobe (n.)
"one suffering from acrophobia," 1895, from acrophobia; also see -phobe.
acrophobia (n.)
"morbid fear of heights," 1887, medical Latin, from Greek akros "at the end, the top" (see acrid) + -phobia "fear." Coined by Italian physician Dr. Andrea Verga in a paper describing the condition, from which Verga himself suffered.
In this paper, read somewhat over a year ago at the congress of alienists at Pavia, the author makes confession of his own extreme dread of high places. Though fearless of the contagion of cholera, he has palpitations on mounting a step-ladder, finds it unpleasant to ride on the top of a coach or to look out of even a first-story window, and has never used an elevator. ["American Journal of Psychology," Nov. 1888, abstract of Verga's report]
acropolis (n.)
1660s, from Greek akropolis "citadel" (especially that of Athens), from akros "highest, upper" (see acrid) + polis "city" (see polis).