atilt (adv.)
"tilted," 1560s, from a- (1) + tilt (v.).
Atlantean (adj.)
1660s, "resembling or pertaining to Atlas" (q.v.). From 1852 as "pertaining to Atlantis" (q.v.).
Atlantic (adj.)
"of or pertaining to the sea off the west coast of Africa," early 15c., Atlantyke, from Latin Atlanticus, from Greek Atlantikos "of Atlas," adjectival form of Atlas (genitive Atlantos), in reference to Mount Atlas in Mauritania (see Atlas). Applied since c. 1600 to the ocean between Europe and Africa, on one side, and the Americas on the other. As a noun late 14c., Athlant, from Old French Atlante.
Atlantis
mythical island-nation, by 1730, from Greek Atlantis, literally "daughter of Atlas," noun use of fem. adjective from Atlas (stem Atlant-; see Atlas). All references trace to Plato's dialogues "Timaeus" and "Critias," both written c. 360 B.C.E.
Atlas
1580s, in Greek mythology a member of the older family of Gods, later regarded as a Titan, son of Iapetus and Clymene; in either case supposed to uphold the pillars of heaven (or earth), which according to one version was his punishment for being the war leader of the Titans in the struggle with the Olympian gods. "Originally the name of an Arcadian mountain god; the name was transferred to the mountain chain in Western Africa" [Beekes].

The Greek name traditionally is interpreted as "The Bearer (of the Heavens)," from a-, copulative prefix (see a- (3)), + stem of tlenai "to bear," from PIE root *tele- "to lift, support, weigh." But Beekes compares Berber adrar "mountain" and finds it plausible that the Greek name is a "folk-etymological reshaping" of this. Mount Atlas, in Mauritania, was important in Greek cosmology as a support of the heavens.
atlas (n.)
"collection of maps in a volume," 1636, first in the title of the English translation of "Atlas, sive cosmographicae meditationes de fabrica mundi" (1585) by Flemish geographer Gerhardus Mercator (1512-1594), who might have been the first to use this word in this way. A picture of the Titan Atlas holding up the world appeared on the frontispiece of this and other early map collections.
atlatl (n.)
Native American throwing stick, 1871, from Nahuatl (Aztecan) atlatl "spear-thrower."
ATM (n.)
1976, acronym for automated teller machine (1974), which was developed in modern form c. 1968. See teller.
atman (n.)
in Hindu philosophy, the self or soul, 1785, from Sanskrit atma "essence, breath, soul," from PIE *etmen "breath" (a root found in Sanskrit and Germanic; source also of Old English æðm, Dutch adem, Old High German atum "breath," Old English eþian, Dutch ademen "to breathe").
atmo-
word-forming element meaning "vapor," from Greek atmos "vapor, steam," from PIE *awet-mo-, from root *wet- (1) "to blow" (also "to inspire, spiritually arouse;" see wood (adj.)).
atmosphere (n.)
1630s, atmosphaera (modern form from 1670s), "gaseous envelop surrounding the earth," from Modern Latin atmosphaera, from Greek atmos "vapor, steam" (see atmo-) + sphaira "sphere" (see sphere). In old science, "vaporous air," which was considered a part of the earth and a contamination of the lower part of the air (n.1).
Þe ouer partye of þe eyr is pure and clene, clere, esy & softe, ffor mevynge of stormys, of wynde and of wedir may nat reche þerto; and so it perteyneþ to heuenlych kynde. And þe neþir partye is nyʒe to þe spere of watir and of erþe, and is troubly, greet and þicke, corpulent and ful of moyst erþy vapoures, as longiþ to erþy partyes. Þe eyr strecchiþ hym kyndely al aboute fro þe ouer partye of þe erþe and of watir anon to þe spere of fire. [John of Trevisa, translation of Bartholomew de Glanville's "De proprietatibus rerum," 1398]
First used in English in connection with the Moon, which, as it turns out, practically has none.
It is observed in the solary eclipses, that there is sometimes a great trepidation about the body of the moon, from which we may likewise argue an atmosphaera, since we cannot well conceive what so probable a cause there should be of such an appearance as this, Quod radii solares a vaporibus lunam ambitntibus fuerint intercisi, that the sun-beams were broken and refracted by the vapours that encompassed the moon. [Rev. John Wilkins, "Discovery of New World or Discourse tending to prove that it probable there may be another World in the Moon," 1638]
Figurative sense of "surrounding influence, mental or moral environment" is c. 1800.
atmospheric (adj.)
1777, "pertaining to or existing in the atmosphere," from atmosphere + -ic. In a sense of "creating a mood or mental environment" it is from 1908. Atmospherics "disturbances in wireless communication" is from 1905.
atoll (n.)
"island consisting of a strip or ring of coral around a central lagoon," 1620s, atollon, from Malayalam (Dravidian) atolu "reef," which is said to be from adal "closing, uniting." Watkins writes, "Perhaps ultimately from Sanskrit antara-, interior" (from PIE root *en "in"). The original use was in reference to the Maldives. Popularized in present form by Darwin's writings.
atom (n.)
late 15c., as a hypothetical indivisible extremely minute body, the building block of the universe, from Latin atomus (especially in Lucretius) "indivisible particle," from Greek atomos "uncut, unhewn; indivisible," from a- "not" (see a- (3)) + tomos "a cutting," from temnein "to cut" (from PIE root *tem- "to cut"). An ancient term of philosophical speculation (in Leucippus, Democritus); revived scientifically 1805 by British chemist John Dalton. In late classical and medieval use also a unit of time, 22,560 to the hour. Atom bomb is from 1945 as both a noun and a verb; compare atomic.
atomic (adj.)
"pertaining to atoms," 1670s as a philosophical term (see atomistic); scientific sense dates from 1811, from atom + -ic. Atomic number is from 1821; atomic mass is from 1848. Atomic energy first recorded 1906 in modern sense (as intra-atomic energy from 1903).
March, 1903, was an historic date for chemistry. It is, also, as we shall show, a date to which, in all probability, the men of the future will often refer as the veritable beginning of the larger powers and energies that they will control. It was in March, 1903, that Curie and Laborde announced the heat-emitting power of radium. [Robert Kennedy Duncan, "The New Knowledge," 1906]
Atomic bomb first recorded 1914 in writings of H.G. Wells ("The World Set Free"), who thought of it as a bomb "that would continue to explode indefinitely."
When you can drop just one atomic bomb and wipe out Paris or Berlin, war will have become monstrous and impossible. [S. Strunsky, "Yale Review," January 1917]
Atomic Age is from 1945. Atomical "concerned with atoms," also "very minute," is from 1640s. Atomic clock is from 1938.
atomies (n.)
1590s, "atoms," also "diminutive beings," from atomy, from Latin atomi, plural of atomus (see atom), but taken as a singular in English and re-pluralized in the native way. Perhaps also in some cases a plural of atomy (from misdivision of anatomy).
atomistic (adj.)
1809, in reference to the classical philosophical or metaphysical doctrine of atomism (1670s); modern sense (logical atomism) traces to 1914 and Bertrand Russell and the philosophy that, "while maintaining that there are many things, ... denies that there is a whole composed of these things."
atomization (n.)
"reduction of liquids to the form of a spray," 1860, noun of action from atomize. Perhaps based on earlier French atomisation.
atomize (v.)
"reduce to atoms," 1829; "reduce a liquid to a very fine mist," 1860, verb formed from atom + -ize. Related: Atomized; atomizing. Originally in reference to medical treatment for injured or diseased lungs; sense of "to destroy with atomic weapons" is from 1945.
atomizer (n.)
"apparatus to reduce liquids to a spray or mist," 1865, agent noun from atomize.
atomy (n.)
see atomies.
Aton
variant of Aten.
atonable (adj.)
1670s, from atone + -able.
atonal (adj.)
in musical composition, "not considering scale or tone," 1911, from a- (3) "not, without" + tonal.
atonality (n.)
1919, in reference to Erik Satie; see atonal + -ity.
atone (v.)
1590s, "be in harmony, agree, be in accordance," from adverbial phrase atonen (c. 1300) "in accord," literally "at one," a contraction of at and one. It retains the older pronunciation of one. Meaning "make up (for errors or deficiencies)" is from 1660s; that of "make reparations" is from 1680s. The phrase perhaps is modeled on Latin adunare "unite," from ad "to, at" (see ad-) + unum "one." Related: Atoned; atoning.
atonement (n.)
1510s, "condition of being at one (with others)," a sense now obsolete, from atone + -ment. Theological meaning "reconciliation" (of man with God through the life, passion, and death of Christ) is from 1520s; that of "satisfaction or reparation for wrong or injury, propitiation of an offended party" is from 1610s.
atop (adv.)
"on or at the top," 1650s, from a- (1) + top (n.1). Two words or hyphenated at first; not fully established as one word till late 19c.
atopic (adj.)
"pertaining to ro characteristic of atopy," 1923, from atopy + -ic.
atopy (n.)
"type of abnormal hypersensitiveness," 1923, coined by Edward D. Perry, professor of Greek at Columbia University, at the request of medical men, from Greek atopia "unusualness, strangeness, a being out of the way," from atopos "out of place, strange, odd, eccentric," from a- "not, without" (see a- (3)) + topos "place" (see topos).
ATP
abbreviation of adenosine triphosphate, attested from 1939.
atrabiliary (adj.)
"melancholic," 1725, from Medieval Latin atrabilarius; an alternative of atrabilious (q.v.). Other alternatives are, or were, atrabilarious (1680s), atrabilarian (1670s), atrabilaric (1620).
atrabilious (adj.)
"affected by melancholy," 1650s, from Latin atra bilis, translating Greek melankholia "black bile" (see melancholy; also compare bile). Atra is fem. of ater "black, dark, gloomy," and is perhaps "blackened by fire," from PIE root *ater- "fire." Related: Atrabiliousness.
atremble (adv.)
1852, from a- (1) + tremble (v.).
atresia (n.)
"occlusion of a natural passage in the body, absence of a natural opening or passage," 1807, from Modern Latin atresia, from Greek atretos "not perforated," from a- "not, without" (see a- (3)) + tresis "perforation," from PIE root *tere- (1) "to rub, turn," with derivatives referring to boring and drilling. Related: Atresic.
Atreus
in Greek mythology, the son of Pelops, father of Agamemnon and Menelaus. Hence Latin Atrides "sons of Atreus."
atria (n.)
classical plural of atrium.
atrial (adj.)
by 1860 in the medical sense "pertaining to one of the atria of the heart," from atrium + -al (1).
atrium (n.)
1570s, from Latin atrium "central court or first main room of an ancient Roman house, room which contains the hearth," from Proto-Italic *atro-, sometimes said (on authority of Varro, "De Lingua Latina") to be Etruscan. Watkins suggests it is from PIE root *ater- "fire," on notion of "place where smoke from the hearth escapes" (through a hole in the roof). De Vaan finds this not very compelling, "since soot is black, but not the fire itself," and prefers a different PIE root, *hert-r- "fireplace," with cognates in Old Irish aith, Welsh odyn "furnace, oven," Avestan atarš "fire."
The appurtenance of atrium depends on the interpretation that this room originally contained the fireplace. This etymology was already current in ancient times, but there is no independent evidence for it. Still, there is no good alternative. [de Vaan]
The anatomical sense of "either of the upper cavities of the heart" first recorded 1870. Meaning "sky-lit central court in a public building" is attested by 1967.
atrocious (adj.)
1660s, "heinous, extremely criminal, enormously cruel," from stem of Latin atrox "fierce, savage, cruel" (see atrocity) + -ous. Weakened colloquial sense "very bad" is late 19c. Related: Atrociously; atrociousness.
atrocity (n.)
1530s, "enormous wickedness," from Middle French atrocité or directly from Latin atrocitatem (nominative atrocitas) "cruelty, fierceness, harshness," noun of quality from atrox "fierce, cruel, frightful," from PIE *atro-ek-, from root *ater- "fire" + root *okw- "to see;" thus "of fiery or threatening appearance." The meaning "an atrocious deed" is from 1793.
atrophic (adj.)
"pertaining to or characterized by atrophy," 1819; see atrophy + -ic.
atrophy (n.)
"a wasting away through lack of nourishment," 1610s (atrophied is from 1590s), from French atrophie, from Late Latin atrophia, from Greek atrophia "a wasting away," abstract noun from atrophos "ill-fed, un-nourished," from a- "not, without" (see a- (3)) + trophe "nourishment," from trephein "to fatten" (see -trophy).
atrophy (v.)
"to waste away," 1808, from atrophy (n.). Related: Atrophied; atrophying.
atropine (n.)
also atropin, "poisonous crystalline alkaloid obtained from nightshade," 1831, from Latin atropa "deadly nightshade" (from which the alkaloid poison is extracted), from Greek atropos "inflexible, unchangeable," also the name of one of the Fates (see Atropos) + chemical suffix -ine (2). By 1821 in French and German.
Atropos
one of the Fates (the one who holds the shears and determines the manner of a person's death and cuts the thread), from Greek, "inflexible, unchangeable," literally "not to be turned away," from a- "not" (see a- (3)) + stem of trepein "to turn" (from PIE root *trep- "to turn"). Related form atropa was the Greek name for deadly nightshade.
attaboy (interj.)
1909, originally in baseball slang, said to be from common pronunciation of "that's the boy!" a cheer of encouragement or approval. I'm the boy for ______ "I'm willing and capable at" is attested from 1843. Related: Attagirl (1924).
attach (v.)
mid-14c. (mid-13c. in Anglo-Latin), "to take or seize (property or goods) by law," a legal term, from Old French atachier "fasten; arrest" (11c.), earlier estachier "to attach, fix; stake up, support" (Modern French attacher, also compare Italian attaccare), from a- "to" (see ad-) + base also found in detatch, perhaps from Frankish *stakon "a post, stake" or a similar Germanic word, from Proto-Germanic *stakon- "a stake," from PIE root *steg- (1) "pole, stick" (see stake (n.)).

Meaning "to fasten, affix, connect," which probably is the original sense etymologically, is attested in English from c. 1400. Related: Attached; attaching.
attachable (adj.)
1570s, "liable to arrest," from attach + -able. Meaning "capable of being tacked on" is attested by 1856.
attache (n.)
1835, from French attaché "junior officer attached to the staff of an ambassador, etc.," literally "attached," noun use of past participle of attacher "to attach" (see attach). Attache case "small leather case for carrying papers" first recorded 1900.