Online Etymology Dictionary

Athenian (n.): Old English Atheniense (plural noun), from Latin Atheniensis, from Athenae (see Athens).
Athens: city of ancient Attica, capital of modern Greece, from Greek Athenai (plural because the city had several distinct parts), traditionally derived from Athena, but probably assimilated from a lost name in a pre-Hellenic language.
atheroma (n.): "encysted tumor," 1706, medical Latin, from Greek atheroma, from athere "groats, porridge" (related to ather "chaff"), in reference to what is inside. For ending, see -oma.
atherosclerosis (n.): 1908, from atherosklerose, coined in German 1904; see atheroma + sclerosis.
athetosis (n.): 1871, from Greek athetos "not fixed, without position or place, set aside" + -osis. Coined by U.S. nerve specialist William Alexander Hammond (1828-1900).
athlete (n.): early 15c., from Latin athleta "a wrestler, athlete, combatant in public games," from Greek athletes "prizefighter, contestant in the games," agent noun from athlein "to contest for a prize," related to athlos "a contest" and athlon "a prize," which is of unknown origin. Before 1750, usually in Latin form. In this sense, Old English had plegmann "play-man." Athlete's foot first recorded 1928, for an ailment that has been around much longer.
athletic (adj.): 1630s (athletical is from 1590s), "pertaining to an athlete," from Latin athleticus, from Greek athletikos, from athletes (see athlete). Meaning "strong of body; vigorous; lusty; robust" [Johnson, who spells it athletick] is from 1650s.
athleticism (n.): 1835, from athletic + -ism.
athletics (n.): c. 1730, from athletic; also see -ics. Probably formed on model of gymnastics.
athrob (adj.): 1857, from a- (1) + throb. Related: Athrobbing.
athwart (adv.): late 15c., from a- (1) + thwart.
atilt (adv.): 1560s, from a- (1) + tilt (n.).
Atlantic: late 14c., occean of Athlant "sea off the west coast of Africa" (early 15c. as occean 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 to the whole ocean since c. 1600.
Atlantis: mythical island-nation, from Greek Atlantis, literally "daughter of Atlas." All references trace to Plato's dialogues "Timaeus" and "Critias," both written c. 360 B.C.E.
Atlas: 1580s, Titan, son of Iapetus and Clymene, supposed to uphold the pillars of heaven, which was his punishment for being the war leader of the Titans in the struggle with the Olympian gods. The name in Greek perhaps means "The Bearer (of the Heavens)," from a-, copulative prefix, + stem of tlenai "to bear," from PIE root *tele- "to lift, support, weigh." 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 reference to 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: 1976, acronym for automated teller machine (1974), which was developed in modern form c. 1968.
atman (n.): 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").
atmosphere (n.): 1630s, atmosphaera (modern form from 1670s), from Modern Latin atmosphaera, from atmo-, comb. form of Greek atmos "vapor, steam" + spharia "sphere" (see sphere). Greek atmos is from PIE *awet-mo-, from root *wet- (1) "to blow" (also "to inspire, spiritually arouse;" see wood (adj.)). First used in English in connection with the Moon, which, as it turns out, practically doesn't have one.
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.): 1783, 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.): 1620s, atollon, from Malayam atolu "reef," probably from adal "closing, uniting." Popularized in present form by Darwin's writings.
atom (n.): late 15c., as a hypothetical indivisible body, the building block of the universe, from Latin atomus (especially in Lucretius) "indivisible particle," from Greek atomos "uncut, unhewn; indivisible," from a- "not" + tomos "a cutting," from temnein "to cut" (see tome). An ancient term of philosophical speculation (in Leucippus, Democritus), revived 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.): 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, 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 is from 1640s.
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 doctrine of atomism (1670s); modern philosophical sense (logical atomism) traces to 1914 and Bertrand Russell.
atomization (n.): 1866, noun of action from atomize.
atomize (v.): "reduce to atoms," 1845; "reduce a liquid to a very fine mist," 1865, 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.): 1865, agent noun from atomize.
Aton: variant of Aten.
atonal (adj.): 1922, from a- "not" (see a- (2)) + tonal.
atonality (n.): 1950; see atonal + -ity.
atone (v.): 1550s, from adverbial phrase atonen (c. 1300) "in accord," literally "at one," a contraction of at and one. It retains the older pronunciation of one. 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)," from atone + -ment. Meaning "reconciliation" (especially of sinners with God) is from 1520s; that of "propitiation of an offended party" is from 1610s.
atop (adv.): 1650s, from a- (1) + top. Two words or hyphenated at first; not fully established as one word till late 19c.
atopic (adj.): 1923, from atopia (see atopy) + -ic.
atopy (n.): 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-, privative prefix (see a- (3)), + topos "place" (see topos).
ATP: abbreviation of adenosine triphosphate, attested from 1939.
atrabiliary (adj.): 1725, from Medieval Latin atrabilarius; see atrabilious.
atrabilious (adj.): 1650s, from Latin atra bilis, translating Greek melankholia "black bile" (see melancholy; also compare bile). Atra is fem. of ater "black, dark, gloomy," perhaps related to root of atrocity. Related: Atrabiliousness.
atremble (adv.): 1852, from a- (1) + tremble (v.).
atresia (n.): "occlusion of a natural passage in the body," 1807, from Modern Latin atresia, from Greek atretos "not perforated," from a-, privative prefix, + tresis "perforation," from PIE *tere- (1) "to rub, turn," with derivatives referring to boring and drilling (see throw (v.)).
Atreus: in Greek mythology, the son of Pelops, father of Agamemnon and Menelaus.
atria (n.): classical plural of atrium.
atrial (adj.): by 1860 in the medical sense, from atrium + -al (1).
atrium (n.): 1570s, from Latin atrium "central court or main room of an ancient Roman house, room which contains the hearth," sometimes said (on authority of Varro, "De Lingua Latina") to be an Etruscan word, but perhaps from PIE *ater- "fire," on notion of "place where smoke from the hearth escapes" (through a hole in the roof). Anatomical sense of "either of the upper cavities of the heart" first recorded 1870. Meaning "skylit central court in a public building" first attested 1967.
atrocious (adj.): 1660s, from stem of Latin atrox "fierce, savage, cruel" (see atrocity) + -ous. Colloquial sense "very bad" is late 19c. Related: Atrociously; atrociousness.
atrocity (n.): 1530s, 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" (see atrium) + *okw- "see" (see eye (n.)); thus "of fiery or threatening appearance." The meaning "an atrocious deed" is from 1793.
atrophic (adj.): 1819; see atrophy + -ic.
atrophy (n.): "a wasting away through lack of nourishment," 1620s (atrophied is from 1590s), from French atrophie, from Late Latin atrophia, from Greek atrophia "a wasting away," noun of state from atrophos "ill-fed, un-nourished," from a- "not" + trophe "nourishment," from trephein "to fatten" (see -trophy).