Online Etymology Dictionary

at-bat (n.): "baseball player's turn at the plate," 1912, originally a column heading in statistics tables.
at-home (n.): "reception of visitors," 1745, from phrase at home.
Atalanta: in Greek mythology the daughter of king Schoeneus, famous for her swiftness, Latin, from Greek Atalante, fem. of atalantos "having the same value (as a man)," from a- "one, together" + talanton "balance, weight, value" (cf. talent).
ataractic (adj.): 1941, from Greek ataraktos "not disturbed" (see ataraxia) + -ic.
ataraxia (n.): also Anglicized as ataraxy, "calmness, impassivity," c.1600, from Modern Latin, from Greek ataraxia "impassiveness," from a-, privative prefix, + tarassein (Attic tarattein) "to disturb, confuse," from PIE root *dher- "to make muddy, darken."
atavic (adj.): "pertaining to a remote ancestor," 1866, from Latin atavus "ancestor" (see atavism) + -ic.
atavism (n.): 1833, from French atavisme, attested by 1820s, from Latin atavus "ancestor, forefather," from at- perhaps here meaning "beyond" + avus "grandfather," from PIE *awo- "adult male relative other than the father" (see uncle).
atavistic (adj.): "pertaining to atavism," 1847; see atavism + -ic.
ataxia (n.): also anglicized as ataxy, "irregularity of bodily functions," 1610s, "confusion, disorder," medical Latin, from Greek ataxia, from a-, privative prefix, + taxis "arrangement, order," from stem of tassein "to arrange" (see tactics). Pathological sense is attested from 1660s.
ataxic (adj.): 1853, from ataxia + -ic.
atchoo: imitative of the sound of sneezing, first attested 1873, as atcha (a-tschoo is from 1878).
ate: past tense of eat (q.v.).
Ate: Greek goddess of infatuation and evil, from ate "infatuation, bane, ruin, mischief," of uncertain origin.
atelectasis (n.): "incomplete expansion of the lungs," 1836, medical Latin, from Greek ateles "imperfect, incomplete," literally "without an end," (from a-, privative prefix, + telos "completion") + ektosis "extention." Related: Atelectatic.
atelier (n.): 1840, from French atelier "workshop," from Old French astelier "(carpenter's) workshop, woodpile" (14c.), from astele "piece of wood, a shaving, splinter," probably from Late Latin hastella "a thin stick," diminutive of hasta "spear, shaft" (see yard (n.2)).
atemporal (adj.): 1870, from a- "not" + temporal. Related: Atemporally.
Aten: a name of the sun in ancient Egypt, from Egyptian itn.
Athabascan: 1846, Athapaskan, from the name of the North American Indian people, from Lake Athabaska in northern Alberta, Canada, from Woods Cree (Algonquian) Athapaskaw, said by Webster to mean literally "grass or reeds here and there," referring to the delta region west of the lake. Also in reference to their language group.
Athanasian (adj.): 1580s, from Athanasius, archbishop of Alexandria in the reign of Constantine. The name is Latin, from Greek Athanasios, from athanatos "immortal," from a- "not," privative prefix, + thanatos "death."
atheism (n.): 1580s, from French athéisme (16c.), from Greek atheos "without god" (see atheist). A slightly earlier form is represented by atheonism (1530s) which is perhaps from Italian atheo "atheist." Ancient Greek atheotes meant "ungodliness."
atheist (n.): 1570s, from French athéiste (16c.), from Greek atheos "without god, denying the gods; abandoned of the gods; godless, ungodly," from a- "without" + theos "a god" (see Thea).
The existence of a world without God seems to me less absurd than the presence of a God, existing in all his perfection, creating an imperfect man in order to make him run the risk of Hell. [Armand Salacrou, "Certitudes et incertitudes," 1943]
atheistic (adj.): 1630s, from atheist + -ic. Atheistical attested from c.1600.
atheling (n.): "member of a noble family," Old English æðling, from æðel "noble family," related to Old English æðele "noble," from Proto-Germanic *athala-, from PIE *at-al- "race, family," from *at(i)- "over, beyond, super" + *al- "to nourish." With suffix -ing "belonging to." A common Germanic word (cf. Old Saxon ediling, Old Frisian etheling, Old High German adaling).
Athelstan: masc. proper name, Old English Æðelstane, literally "noble stone;" see atheling + stone (n.).
Athena: Greek goddess of wisdom, skill in the arts, warfare, etc., from Latin Athena, from Greek Athene, perhaps from a name in a lost pre-Hellenic language.
Athenaeum (n.): 1727, from Latinized form of Greek Athenaion "(the temple of) Athene," in ancient Athens, in which professors taught and actors or poets rehearsed. Meaning "literary club-room or reading room" is from 1799; "literary or scientific club" is from 1864.
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," 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 (Aztec) 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, cf. 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- "to blow, inspire, spiritually arouse" (see wood (adj.)). First used in English in connection with the Moon, which, as it turns out, 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; cf. 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.