Online Etymology Dictionary

aggrieved (adj.): "oppressed in spirit," mid-14c., past participle adjective from aggrieve. The legal sense of "injured or wronged in one's rights" is from 1580s.
aghast (adj.): c. 1300, agast, "terrified," past participle of Middle English agasten "to frighten" (c. 1200), from a- intensive prefix + Old English gæstan "to terrify," from gæst "spirit, ghost" (see ghost). The -gh- spelling appeared early 15c. in Scottish and is possibly a Flemish influence, or after ghost, etc. It became general after 1700.
agile (adj.): 1580s, from Middle French agile (14c.) and directly from Latin agilis "nimble, quick," from agere "to move, drive" (see act (n.)). Related: Agilely.
agility (n.): early 15c., from Old French agilité (14c.), from Latin agilitatem (nominative agilitas) "mobility, nimbleness, quickness," from agilis, from agere "to move" (see act (n.)).
agism (n.): alternative spelling of ageism.
agitate (v.): 1580s, "to disturb," from Latin agitatus, past participle of agitare "to put in constant motion, drive onward, impel," frequentative of agere "to move, drive" (see act (n.)). Literal sense of "move to and fro, shake" is from 1590s. Related: Agitated; agitating.
agitated (adj.): 1610s, "set in motion," past participle adjective from agitate (v.). Meaning "disturbed" is from 1650s; that of "disturbed in mind" is from 1756. Meaning "kept constantly in public view" is from 1640s.
agitation (n.): 1560s, "mental tossing to and fro," from French agitation, from Latin agitationem (nominative agitatio) "motion, agitation," noun of action from past participle stem of agitare "move to and fro," frequentative of agere in its sense of "to drive" (see act (n.)).
agitator (n.): 1640s, agent noun from agitate (v.); originally "elected representative of the common soldiers in Cromwell's army," who brought grievances (chiefly over lack of pay) to their officers and Parliament.

Political sense is first recorded 1734, and negative overtones began with its association with Irish patriots such as Daniel O'Connell (1775-1847). Historically, in American English, often with outside and referring to people who stir up a supposedly contented class or race. Latin agitator meant "a driver, a charioteer."
agitprop (n.): also agit-prop, 1938, from Russian agitatsiya "agitation" (from French agitation; see agitation) + propaganda, from German (see propaganda).
Aglaia: one of the Graces, Greek, literally "splendor, beauty, brightness," from aglaos "splendid, beautiful, bright," which is of unknown origin, + abstract noun ending -ia.
agleam (adj.): 1854, from a- (1) + gleam.
aglow (adj.): 1817 (in Coleridge), from a- (1) + glow. Figurative sense of "flushed with pleasurable excitement" is from 1830.
Agnes: fem. proper name, mid-12c., from Old French Agnes, from Greek Hagne "pure, chaste," from fem. of hagnos "holy," from PIE *yag- "to worship, reverence" (see hagiology). St. Agnes, martyred 303 C.E., is patron saint of young girls, hence the folk connection of St. Agnes' Eve (Jan. 20-21) with love divinations. In Middle English, frequently phonetically as Annis, Annys. In U.S., among the top 50 names for girls born between 1887 and 1919.
agnostic (n.): 1870, "one who professes that the existence of a First Cause and the essential nature of things are not and cannot be known" [Klein]; coined by T.H. Huxley (1825-1895), supposedly in September 1869, from Greek agnostos "unknown, unknowable," from a- "not" + gnostos "(to be) known" (see gnostic). Sometimes said to be a reference to Paul's mention of the altar to "the Unknown God," but according to Huxley it was coined with reference to the early Church movement known as Gnosticism (see Gnostic).
I ... invented what I conceived to be the appropriate title of 'agnostic,' ... antithetic to the 'Gnostic' of Church history who professed to know so much about the very things of which I was ignorant. [T.H. Huxley, "Science and Christian Tradition," 1889]
The adjective is first recorded 1870.
agnosticism (n.): 1870, from agnostic + -ism.
The agnostic does not simply say, "I do not know." He goes another step, and he says, with great emphasis, that you do not know. [Robert G. Ingersoll, "Reply to Dr. Lyman Abbott," 1890]
Agnus Dei: Latin, literally "lamb of God." Latin agnus is from PIE *agwh-no- "lamb" (see yean) For deus "god," see Zeus.
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," which is 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 "contend in the struggle" (see agony). Intransitive sense of "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," corresponding to 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- (source also of 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. To do the agreeable (1825) was to "act in a courteous manner."
agreeance (n.): 1530s, from Middle French agréance, noun of action from agréer (see agree).
agreement (n.): 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 could be 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 numismatic). 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 "acute fever," from Medieval Latin (febris) acuta "sharp (fever)," with 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 Aesir) + Avestan mazda- "wise," from PIE *mens-dhe- "to set the mind," from root *men- "to think" (see mind (n.)).
aid (n.): 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.): 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), which is French and means "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.