Online Etymology Dictionary

ago (adj.): early 14c., shortened form of Old English agan, agone "departed, passed away," past participle of an obsolete verb ago "to go forth," formed from a- "away" (perhaps here used as an intensive prefix) + gan "go" (see go (v.)). Agone remains a dialectal variant.
agog (adj., adv.): "in a state of desire; in a state of imagination; heated with the notion of some enjoyment; longing" [Johnson], c.1400, perhaps from Old French en gogues "in jest, good humor, joyfulness," from gogue "fun," of unknown origin.
agonist (n.): 1876, in writings on Greek drama, from Greek agonistes, literally "combatant in the games" (see agony).
agonize (v.): 1580s, "to torture," from Middle French agoniser or directly from Medieval Latin agonizare, from Greek agonizesthai "to contend in the struggle" (see agony). Intransitive sense of "to suffer physical pain" is recorded from 1660s. That of "to worry intensely" is from 1853. Related: Agonized; agonizing.
agony (n.): late 14c., "mental suffering" (especially that of Christ in the Garden of Gethsemane), from Old French agonie, agoine "anguish, terror, death agony" (14c.), and directly from Late Latin agonia, from Greek agonia "a (mental) struggle for victory," originally "a struggle for victory in the games," from agon "assembly for a contest," from agein "to lead" (see act (n.)). Sense of "extreme bodily suffering" first recorded c.1600.
agora (n.): "assembly place," 1590s, from Greek agora "open space" (typically a marketplace), from ageirein "to assemble," from PIE root *ger- "to gather" (see gregarious).
agoraphobia (n.): "fear of open spaces," 1873, from German Agorophobie, coined 1871 by Berlin psychiatrist Carl Westphal (1833-1890) from Greek agora "open space" (see agora) + -phobia "fear." Related: Agoraphobe; agoraphobic.
agrarian (adj.): 1610s, "relating to the land," from Middle French loy agrarienne "agrarian law," from Latin Lex agraria, the Roman law for the division of conquered lands, from agrarius "of the land," from ager (genitive agri) "a field," from PIE *agro- (cf. Greek agros "field," Gothic akrs, Old English æcer "field;" see acre). Meaning "having to do with cultivated land" first recorded 1792.
agree (v.): late 14c., "to be to one's liking;" also "to give consent," from Old French agreer "to receive with favor, take pleasure in" (12c.), from phrase a gré "favorably, of good will," literally "to (one's) liking," from Latin ad "to" (see ad-) + gratum "pleasing," neuter of gratus (see grace (n.)); the original sense survives best in agreeable. Meaning "to be in harmony in opinions" is from late 15c. Related: Agreed; agreeing.
agreeable (adj.): late 14c., "to one's liking," from Old French agreable (12c., Modern French agréable) "pleasing, in agreement, consenting, thankful," from agreer "to please" (see agree). Related: Agreeably.
agreeance (n.): 1530s, from Middle French agréance, noun of action from agréer (see agree).
agreement (n.): late 14c., "mutual conformity of things;" c.1400, "mutual understanding" (among persons), also (of things) "mutual conformity," from Old French agrement, noun of action from agreer "to please" (see agree).
agribusiness (n.): 1955, compound formed from agriculture + business.
agricultural (adj.): 1776, from agriculture + -al (1). Related: Agriculturally; agriculturalist.
agriculture (n.): mid-15c., from Late Latin agricultura "cultivation of the land," compound of agri cultura "cultivation of land," from agri, genitive of ager "a field" (see acre) + cultura "cultivation" (see culture (n.)). In Old English, the idea was expressed by eorðtilþ.
agriology (n.): study of prehistoric human customs, 1878, from agrio-, from Greek agrios "wild," literally "living in the fields," from agros "field" (see acre) + -logy. Related: Agriologist (n.), 1875.
agro-: word-forming element meaning "pertaining to agriculture or cultivation," from Greek agro-, comb. form of agros "field" (see acre).
agronomy (n.): "science of land management for crop production," 1814, from French agronomie, from Greek agronomos "overseer of land," from agros "field" (see acre) + -nomos "law or custom, administering," related to nemein "manage" (see numismatics). Related: Agronomist; agronomic.
aground (adv.): late 13c., "on the ground," from a- "on" (see a- (1)) + ground (n.). Of ships and boats, "stranded," from c.1500.
ague (n.): "malarial fever," c.1300, from Old French ague "an acute fever," from Medieval Latin (febris) acuta "sharp (fever)," fem. of acutus "sharp" (see acute).
ah: mid-15c., an expression of surprise, delight, disgust or pain in nearly all Indo-European languages, but not found in Old English (where the equivalent expression was la!), so perhaps from Old French a "ah!, oh! woe!"
aha: exclamation of surprise or delighted discovery, late 14c., from ah + ha.
They crieden out! ... A ha the fox! and after him thay ran. [Chaucer]
ahead (adv.): 1620s, "at the head, in front," from a- "on" (see a- (1)) + head (n.). Originally nautical. To be ahead of (one's) time attested by 1837.
ahem: attention-getting interjection, 1763, lengthened from hem, imitative of clearing the throat.
ahimsa (n.): 1875, from Sanskrit ahimsa, from a "without" + himsa "injury."
ahistoric (adj.): "not historical, lacking in historical background or justification," 1911, from a- (2) "not" + historic.
ahistorical (adj.): "without reference to or regard for history," 1950, from a- (2) "not" + historical.
ahoy: 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: from Avestan ahura- "spirit, lord," from Indo-Iranian *asuras, from suffixed form of PIE root *ansu- "spirit" (see Asgard) + Avestan mazda- "wise," from PIE *mens-dhe- "to set the mind," from root *men- "to think" (see mind (n.)).
aid (n.): early 15c., "wartime 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.): 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.): 1777, short for aide-de-camp (1660s), French, literally "camp assistant" (see aid (n.)).
AIDS (n.): 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.): "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, itself a diminutive of Latin acus "needle" (see acuity). Cf. Italian agucchia, Portuguese agulha, Spanish aguja "needle."
aikido (n.): Japanese art of self-defense, 1936, literally "way of adapting the spirit," from Japanese ai "together" + ki "spirit" + do "way, art," from Chinese tao "way."
ail (v.): c.1300, from Old English eglan "to trouble, plague, afflict," from Proto-Germanic *azljaz (cf. 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- "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.): "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.): 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.): 1706, from ail + -ment.
ailurophile (n.): "cat lover," 1931, from Greek ailouros "cat," of unknown origin, + -phile.
ailurophobia (n.): "morbid fear of cats," 1905, from -phobia "fear" + ailouros "cat," of unknown origin. Folk etymology connects it with aiolos "quick-moving" + oura "tail." Related: Ailurophobe (1914).
aim (v.): 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.): 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.): 1620s, from aim (n.) + -less. Related: Aimlessly; aimlessness.
ain't: 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: 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; but DNA testing has disproven this. Their language is an isolate with no known relatives.
air (v.): "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 (n.1): 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"), 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 (e.g. on the air) first recorded 1927. To give (someone) the air "dismiss" is from 1900. Air pollution is attested by 1870.
air (n.2): 1590s, "manner, appearance" (e.g. 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.; cf. 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); cf. sense development of atmosphere and Latin spiritus "breath, breeze," also "high spirit, pride," and the extended senses of anima.
air (n.3): "melody, tune," 1580s, from Italian aria (see aria).