at (prep.)
Old English æt, from Proto-Germanic *at (cognates: Old Norse, Gothic at, Old Frisian et, Old High German az), from PIE *ad- "to, near, at" (cognates: Latin ad "to, toward" Sanskrit adhi "near;" see ad-).

Lost in German and Dutch, which use their equivalent of to; in Scandinavian, however, to has been lost and at fills its place. In choosing between at church, in church, etc. at is properly distinguished from in or on by involving some practical connection; a worshipper is at church; a tourist is in the church.

The colloquial use of at after where ("where it's at") is attested from 1859. At last is recorded from late 13c.; adverbial phrase at least was in use by 1775. At in Middle English was used freely with prepositions (as in at after, which is in Shakespeare), but this has faded with the exception of at about, which was used in modern times by Trollope, Virginia Woolfe, D.H. Lawrence, and Evelyn Waugh, but nonetheless is regarded as a sign of incompetent writing by my copy editor bosses.
at all
"in any way," mid-14c., originally used only affirmatively (as in I Sam. XX:6 in KJV: "If thy father at all misse me"); now it is overwhelmingly used only in the negative or in interrogatory expressions, or in literary attempts at Irish dialect.
at bay
late 14c., originally often at the bay; see bay (n.3). Figurative use, of human beings in difficulties, is from c.1400. The expression reflects the former more widespread use of at. Earlier the expression be at abai was used of the hunted animal, "be unable to escape," c.1300, from French.
at-
assimilated form of ad- "to, toward, before" before stems beginning in -t-; see ad-.
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" (compare talent).
ataractic (adj.)
1941, from Greek ataraktos "not disturbed" (see ataraxia) + -ic.
ataraxia (n.)
also Englished 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- (1) "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" (see thanatology).
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 theo-).
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 (cognates: 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 (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; cognates: 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.