ahoy Look up ahoy at Dictionary.com
1751, from a + hoy, a nautical call used in hauling. The original form of the greeting seems to have been ho, the ship ahoy!
Ahura Mazda Look up Ahura Mazda at Dictionary.com
from Avestan ahura- "spirit, lord," from Indo-Iranian *asuras, from suffixed form of PIE root *ansu- "spirit" (see Aesir) + Avestan mazda- "wise," from PIE *mens-dhe- "to set the mind," from root *men- "to think" (see mind (n.)).
aid (n.) Look up aid at Dictionary.com
early 15c., "war-time tax," also "help, support, assistance," from Old French aide, earlier aiudha "aid, help, assistance" (9c.), from Late Latin adjuta, from fem. past participle of Latin adiuvare (past participle adiutus) "to give help to," from ad- "to" (see ad-) + iuvare "to help" (see adjutant). Meaning "thing by which assistance is given" is recorded from c. 1600. Meaning "material help given by one country to another" is from 1940.
aid (v.) Look up aid at Dictionary.com
c. 1400, "to assist, help," from Old French aidier "help, assistance," from Latin adiutare, frequentative of adiuvare (past participle adiutus) "give help to" (see adjutant). Related: Aided; aiding.
aide (n.) Look up aide at Dictionary.com
1777, short for aide-de-camp (1660s), which is French and means "camp assistant" (see aid (n.)).
AIDS (n.) Look up AIDS at Dictionary.com
1982, acronym formed from acquired immune deficiency syndrome. AIDS cocktail attested by 1997, the thing itself said to have been in use from 1995.
aiglet (n.) Look up aiglet at Dictionary.com
"metal tag of a lace," meant to make it easier to thread through the eyelet-holes, but later merely ornamental, mid-15c., from Middle French aiguillette, diminutive of aiguille "needle," from Late Latin acucula, an extended form (via diminutive suffix, but not necessarily implying smallness) of Latin acus "needle" (see acuity). Compare Italian agucchia, Portuguese agulha, Spanish aguja "needle."
aikido (n.) Look up aikido at Dictionary.com
Japanese art of self-defense, 1936, literally "way of adapting the spirit," from Japanese ai "together" (from au "to harmonize") + ki "spirit" + do "way, art," from Chinese tao "way."
ail (v.) Look up ail at Dictionary.com
c. 1300, from Old English eglan "to trouble, plague, afflict," from Proto-Germanic *azljaz (source also of Old English egle "hideous, loathsome, troublesome, painful;" Gothic agls "shameful, disgraceful," agliþa "distress, affliction, hardship," us-agljan "to oppress, afflict"), from PIE *agh-lo-, suffixed form of root *agh- (1) "to be depressed, be afraid." Related: Ailed; ailing; ails.
It is remarkable, that this word is never used but with some indefinite term, or the word no thing; as What ails him? ... Thus we never say, a fever ails him. [Johnson]
ailanthus (n.) Look up ailanthus at Dictionary.com
"tree of heaven," 1807, Modern Latin, from Amboyna (Malay) ailanto "tree of the gods;" spelling altered by influence of Greek anthos "flower" (see anther).
aileron (n.) Look up aileron at Dictionary.com
1909, from French aileron, altered (by influence of aile "wing"), from French aleron "little wing," diminutive of Old French ele "wing" (12c.), from Latin ala "wing" (see aisle).
ailment (n.) Look up ailment at Dictionary.com
1706, from ail + -ment.
ailurophile (n.) Look up ailurophile at Dictionary.com
"cat lover," 1931, from Greek ailouros "cat," which is of unknown origin, + -phile.
ailurophobia (n.) Look up ailurophobia at Dictionary.com
"morbid fear of cats," 1905, from -phobia "fear" + ailouros "cat," which is of unknown origin. Folk etymology connects it with aiolos "quick-moving" + oura "tail." Related: Ailurophobe (1914).
aim (v.) Look up aim at Dictionary.com
early 14c., "to estimate, calculate," also "to intend," from Old French aesmer "value, rate; count, estimate," from Latin aestimare "appraise" (see estimation); current meaning apparently developed from "esteem," to "calculate," to "calculate with a view to action" (c. 1400), then to "direct a missile, a blow, etc." (1570s). Related: Aimed; aiming.
aim (n.) Look up aim at Dictionary.com
early 14c., "target;" late 14c., "guess;" from aim (v.). Meaning "action of aiming" is from early 15c. (to take aim, originally make aim); that of "thing intended, purpose" is from 1620s.
aimless (adj.) Look up aimless at Dictionary.com
1620s, from aim (n.) + -less. Related: Aimlessly; aimlessness.
ain't Look up ain't at Dictionary.com
1706, originally a contraction of am not, and in proper use with that sense until it began to be used as a generic contraction for are not, is not, etc., in early 19c. Cockney dialect of London; popularized by representations of this in Dickens, etc., which led to the word being banished from correct English.
Ainu Look up Ainu at Dictionary.com
people native to northern Japan and far eastern Russia, 1819, from the Ainu self-designation, literally "man, human." Once considered to be Caucasian, based on their appearance; DNA testing has disproved this. Their language is an isolate with no known relatives.
air (n.1) Look up air at Dictionary.com
c. 1300, "invisible gases that make up the atmosphere," from Old French air "atmosphere, breeze, weather" (12c.), from Latin aerem (nominative aer) "air, lower atmosphere, sky," from Greek aer (genitive aeros) "air" (related to aenai "to blow, breathe"), which is of unknown origin, possibly from a base *awer- and thus related to aeirein "to raise" and arteria "windpipe, artery" (see aorta) on notion of "lifting, that which rises." In Homer mostly "thick air, mist;" later "air" as one of the four elements.

Words for "air" in Indo-European languages tend to be associated with wind, brightness, sky. In English, air replaced native lyft, luft (see loft (n.)). To be in the air "in general awareness" is from 1875; up in the air "uncertain, doubtful" is from 1752. To build castles in the air is from 1590s (in 17c. English had airmonger "one preoccupied with visionary projects"). Broadcasting sense (as in on the air) first recorded 1927. To give (someone) the air "dismiss" is from 1900. Air pollution is attested by 1870.
air (n.2) Look up air at Dictionary.com
1590s, "manner, appearance" (as in an air of mystery); 1650s, "assumed manner, affected appearance" (especially in phrase put on airs, 1781), from French air "look, appearance, mien, bearing, tone" (Old French aire "reality, essence, nature, descent, extraction," 12c.; compare debonair), from Latin ager "place, field" (see acre) on notion of "place of origin."

But some French sources connect this Old French word with the source of air (n.1), and it also is possible these senses in English developed from or were influenced by air (n.1); compare sense development of atmosphere and Latin spiritus "breath, breeze," also "high spirit, pride," and the extended senses of anima.
air (n.3) Look up air at Dictionary.com
"melody, tune," 1580s, from Italian aria (see aria).
air (v.) Look up air at Dictionary.com
"to expose to open air," 1520s, from air (n.1). Figurative sense of "to expose, make public" is from 1610s of objects, 1862 of opinions, grievances, etc. Meaning "to broadcast" (originally on radio) is from 1933. Related: Aired; airing.
air conditioner (n.) Look up air conditioner at Dictionary.com
from air (n.1) + agent noun from condition; along with air-conditioning, first attested 1909, originally an industrial process; main modern use in residences and office buildings is from 1930s.
air force (n.) Look up air force at Dictionary.com
1917, from air (n.1) + force (n.); first attested with creation of the Royal Air Force. There was no United States Air Force until after World War II. The Air Corps was an arm of the U.S. Army. In 1942, the War Department reorganized it and renamed it Army Air Forces. The National Security Act of 1947 created the Department of the Air Force, headed by a Secretary of the Air Force, and the U.S.A.F.
air freshener (n.) Look up air freshener at Dictionary.com
1949, from air (n.1) + agent noun from freshen.
air mail (n.) Look up air mail at Dictionary.com
also air-mail, 1913, from air (n.1) + mail (n.1).
air raid (n.) Look up air raid at Dictionary.com
1914, from air (n.1) + raid (n.); originally in reference to British attacks Sept. 22, 1914, on Zeppelin bases at Cologne and Düsseldorf in World War I. The German word is Fliegerangriff "aviator-attack," and if Old English had survived into the 20th century our word instead might be fleogendeongrype.
One didn't dare to inhale for fear of breathing it in. It was the sound of eighteen hundred airplanes approaching Hamburg from the south at an unimaginable height. We had already experienced two hundred or even more air raids, among them some very heavy ones, but this was something completely new. And yet there was an immediate recognition: this was what everyone had been waiting for, what had hung for months like a shadow over everything we did, making us weary. It was the end. [Hans Erich Nossack, "Der Untergang," 1942]
airborne (adj.) Look up airborne at Dictionary.com
1640s, "carried through the air," from air (n.1) + borne. Of military units, from 1937.
aircraft (n.) Look up aircraft at Dictionary.com
1851, originally in reference to airships and balloons, from air (n.1) + craft (n.); a term from boating, as were many early aviation words. Of airplanes from 1907 and since 1930s exclusively of them. Aircraft carrier is attested from 1919 (H.M.S. Hermes, launched September 1919, was the first ship to be built from the hull up as an aircraft carrier).
Airedale Look up Airedale at Dictionary.com
type of terrier, 1880, named for Airedale, a district in West Riding, Yorkshire.
Name registered by Kennel Club (1886), for earlier Bingley (where first bred), or broken-haired terrier. [Weekley]
airfoil (n.) Look up airfoil at Dictionary.com
1922, U.S. form of aerofoil.
airhead (n.) Look up airhead at Dictionary.com
"empty-headed person," 1972, from air (n.1) + head (n.). Earlier as a term in mining (mid-19c.) and as a military term based on beachhead (1950).
airily (adv.) Look up airily at Dictionary.com
1766, from airy "with ostentatious air" (see air (n.2)) + -ly (2).
airing (n.) Look up airing at Dictionary.com
"action of exposing to air," c. 1600, from present participle of air (v.). Meaning "display, public exposure is from 1870.
airlift (n.) Look up airlift at Dictionary.com
also air-lift, 1893 as a type of pumping device; 1945 in the sense "transportation of supplies by air," from air (n.1) + lift (n.). As a verb by 1949; popularized in reference to the response to the West Berlin blockade. Related: Air-lifted; air-lifting.
airline (n.) Look up airline at Dictionary.com
also air-line, 1813, "beeline, straight line between two points on the earth's surface" (as through the air, rather than over terrain; from 1853 and in later 19c. especially in reference to railways that ran directly between big cities in the U.S. instead of meandering from town to town in search of stock subscriptions as early railways typically did), from air (n.1) + line (n.). Meaning "public aircraft transportation company" is from 1914.
airplane (n.) Look up airplane at Dictionary.com
1907, from air (n.1) + plane (n.1); though the original references are British, the word caught on in American English, where it largely superseded earlier aeroplane (1873 in this sense and still common in British English). Aircraft "airplane" also is from 1907. Lord Byron, speculatively, used air-vessel (1822).
airplay (n.) Look up airplay at Dictionary.com
1950 in radio sense, from air (n.1) + play.
airport (n.) Look up airport at Dictionary.com
1919, from air (n.1) + port (n.1). First reference is to Bader Field, outside Atlantic City, New Jersey, U.S., which opened in 1910.
airship (n.) Look up airship at Dictionary.com
also air-ship, 1888, translating German Luftschiff "motor-driver dirigible;" see air (n.1) + ship (n.).
airtight (adj.) Look up airtight at Dictionary.com
also air-tight, "impervious to air," 1760, from air (n.1) + tight. Figurative sense of "incontrovertible" (of arguments, alabis, etc.) is from 1929.
airy (adj.) Look up airy at Dictionary.com
late 14c., "of the air, made of air," from air (n.1) + -y (2). Meaning "breezy" is attested from 1590s; that of "lively" is from 1640s. Sense of "vain, unsubstantial" is from 1580s. Disparaging airy-fairy is attested from 1920 (earlier in a sense of "delicate or light as a fairy," which is how Tennyson used it in 1830).
aisle (n.) Look up aisle at Dictionary.com
late 14c., ele, "lateral division of a church (usually separated by a row of pillars), from Old French ele "wing (of a bird or an army), side of a ship" (12c., Modern French aile), from Latin ala, related to axilla "wing, upper arm, armpit; wing of an army," from PIE *aks- "axis" (see axis), via a suffixed form *aks-la-. The root meaning in "turning" connects it with axle and axis.

Confused from 15c. with unrelated ile "island" (perhaps from notion of a "detached" part of a church), and so it took an -s- when isle did, c. 1700; by 1750 it had acquired an a-, on the model of French cognate aile. The word also was confused with alley, which gave it the sense of "passage between rows of pews or seats" (1731), which was thence extended to railway cars, theaters, etc.
ajar (adv.) Look up ajar at Dictionary.com
"slightly open," 1718, also on a jar, on the jar, perhaps from Scottish dialectal a char "turned a little way," earlier on char (early 16c.), "on the turn (of a door or gate)," from Middle English char, from Old English cier "a turn."
Ajax Look up Ajax at Dictionary.com
name of two Greek heroes in the Trojan War (Great Ajax, son of Telamon, and Little Ajax, son of Oileus), Latin, from Greek Aias, perhaps originally the name of an earth-god, from aia "earth." The Elizabethans punned on the name as a jakes "a privy."
akimbo Look up akimbo at Dictionary.com
c. 1400, in kenebowe, of unknown origin, perhaps from Middle English phrase in keen bow "at a sharp angle," or from a Scandinavian word akin to Icelandic kengboginn "bow-bent," but this seems not to have been used in this exact sense. Many languages use a teapot metaphor for this, such as French faire le pot a deux anses "to play the pot with two handles."
akin (adj.) Look up akin at Dictionary.com
1550s, from phrase of kin; see kin.
Akita Look up Akita at Dictionary.com
type of dog, named for a prefecture in northern Japan.
Akkadian Look up Akkadian at Dictionary.com
1855, from Akkad (Sumerian Agde, Biblical Acca), name of city founded by Sargon I in northern Babylonia, which is of unknown origin; applied by modern scholars to the east Semitic language spoken there (c. 2300-2100 B.C.E.) and preserved in cuneiform inscriptions.