Online Etymology Dictionary

age (v.): "to grow old," late 14c., from age (n.). Meaning "to make old" is early 15c. Related: Aged; aging.
age-group (n.): 1904, originally a term in the science of demographics, from age (n.) + group (n.).
age-old (adj.): 1896, from age (n.) + old.
aged (adj.): "having lived long," mid-15c., past participle adjective from age (v.). Meaning "having been allowed to get old" (of cheese, etc.) is by 1873. Meaning "of the age of" is from 1630s. Aged Parent is from "Great Expectations" (1860-61).
ageism (n.): "discrimination against people based on age," coined 1969 by U.S. gerontologist Dr. Robert N. Butler, from age + -ism, on pattern of racism, sexism. Related: Ageist.
ageless (adj.): 1650s, from age + -less. Related: Agelessly; agelessness.
agency (n.): 1650s, "active operation," from Medieval Latin agentia, noun of state from Latin agentem (nominative agens) "effective, powerful," present participle of agere (see act (n.)). Meaning "establishment where business is done for another" first recorded 1861.
agenda (n.): 1650s, from Latin agenda, literally "things to be done," neuter plural of agendus, gerundive of agere "to do" (see act (n.)). Originally theological (opposed to matters of belief), sense of "items of business to be done at a meeting" first attested 1882. "If a singular is required (=one item of the agenda) it is now agendum, the former singular agend being obsolete" [Fowler].
agent (n.): late 15c., "one who acts," from Latin agentem (nominative agens) "effective, powerful," present participle of agere "to set in motion, drive, lead, conduct" (see act (n.)). Meaning "any natural force or substance which produces a phenomenon" is from 1550s. Meaning "deputy, representative" is from 1590s. Sense of "spy, secret agent" is attested by 1916.
agent (adj.): 1610s, from agent (n.).
Agent Orange (n.): powerful defoliant used by U.S. military in the Vietnam War, attested from 1971, said to have been used from 1961; so called from the color strip on the side of the container, which distinguished it from Agent Blue, Agent White, etc., other herbicides used by the U.S. military. Banned from April 1970.
aggie (n.1): "college student studying agriculture," by 1880, American English college slang, from agriculture + -ie.
aggie (n.2): type of toy marble, by 1905, American English, colloquial shortening of agate (q.v.).
Excited groups gather about rude circles scratched in the mud, and there is talk of "pureys," and "reals," and "aggies," and "commies," and "fen dubs!" There is a rich click about the bulging pockets of the boys, and every so often in school time something drops on the floor and rolls noisily across the room. When Miss Daniels asks: "Who did that?" the boys all look so astonished. Who did what pray tell? ["McClure's Magazine," May 1905]
agglomerate (v.): 1680s, from Latin agglomeratus, past participle of agglomerare "to wind or add onto a ball," from ad- "to" (see ad-) + glomerare "wind up in a ball," from glomus (genitive glomeris) "ball of yarn," from PIE root *glem-. Related: Agglomerated; agglomerating.
agglomeration (n.): 1774, "action of collecting in a mass," from Latin agglomerationem (nominative agglomeratio), noun of action from past participle stem of agglomerare (see agglomerate). In reference to a mass so formed, it is recorded from 1833.
agglutinate (v.): 1580s (from 1540s as a past participle adjective), from Latin agglutinatus, past participle of agglutinare (see agglutination). Related: Agglutinated; agglutinating.
agglutination (n.): 1540s, from Latin agglutinationem (nominative agglutinatio), noun of action from past participle stem of agglutinare "fasten with glue," from ad- "to" (see ad-) + glutinare "to glue," from gluten "glue," from PIE *glei- (see glue (n.)). Philological sense first recorded 1650s, in agglutinative.
agglutinative (adj.): 1630s, in a medical sense, from Latin agglutinat-, past participle stem of agglutinare (see agglutination). Philological sense is from 1650s.
aggrandisement (n.): chiefly British English spelling of aggrandizement. See -ize.
aggrandize (v.): 1630s, "to make larger, increase," from French agrandiss-, present participle stem of agrandir "to augment" (16c.), ultimately from Latin ad "to" (see ad-) + grandire "to make great," from grandis (see grand (adj.)). The double -g- spelling in English is by analogy with Latin words in ad-. Related: Aggrandized; aggrandizing.
aggrandizement (n.): 1650s, from French agrandissement, noun of action from agrandir (see aggrandize).
aggravate (v.): 1520s, "make heavy, burden down," from past participle adjective aggravate "burdened; threatened" (late 15c.), from Latin aggravatus, past participle of aggravare "to render more troublesome," literally "to make heavy" (see aggravation). Earlier in this sense was aggrege (late 14c.). Meaning "to make a bad thing worse" is from 1590s; that of "exasperate, annoy" is from 1610s.
To aggravate has properly only one meaning -- to make (an evil) worse or more serious. [Fowler]
Related: Aggravated; aggravating. Phrase aggravating circumstances is recorded from 1790.
aggravated (adj.): 1540s, "increased, magnified," past participle adjective from aggravate. Meaning "irritated" is from 1610s; that of "made worse" is from 1630s. The earlier adjective was simply aggravate (late 15c.).
aggravation (n.): late 15c., from Middle French aggravation, from Late Latin aggravationem (nominative aggravatio), noun of action from past participle stem of Latin aggravare "make heavier," figuratively "to embarrass further, increase in oppressiveness," from ad "to" (see ad-) + gravare "weigh down," from gravis "heavy" (see grave (adj.)). Oldest sense is "increasing in gravity or seriousness;" that of "irritation" is from 1610s.
aggregate (adj.): c.1400, from Latin aggregatus "associated," literally "united in a flock," past participle of aggregare "add to (a flock), lead to a flock, bring together (in a flock)," from ad- "to" (see ad-) + gregare "herd" (see gregarious).
aggregate (v.): c.1400, from Latin aggregatum, neuter past participle of aggregare (see aggregate (adj.)). Related: Aggregated; aggregating.
aggregate (n.): "number of persons, things, etc., regarded as a unit," early 15c., from noun use of Latin adjective aggregatum, neuter of aggregatus (see aggregate (adj.)).
aggregation (n.): early 15c., from Middle French agrégation or directly from Medieval Latin aggregationem (nominative aggregatio), noun of action from past participle stem of Latin aggregare (see aggregate (adj.)).
aggress (v.): "attack," 1714, back-formation from aggression, but used earlier with a sense of "approach" (1570s) and in this sense from French aggresser, from Late Latin aggressare, frequentative of Latin aggredi "to approach, attack." Related: Aggressed; aggressing.
aggression (n.): 1610s, "unprovoked attack," from French aggression (16c.), from Latin aggressionem (nominative aggressio) "a going to, an attack," noun of action from past participle stem of aggredi "to approach; attack," from ad- "to" (see ad-) + gradi (past participle gressus) "to step," from gradus "a step" (see grade). Psychological sense of "hostile or destructive behavior" first recorded 1912 in A.A. Brill's translation of Freud.
aggressive (adj.): 1791, from Latin aggress-, past participle stem of aggredi (see aggression) + -ive. In psychological use from 1913, first in translations of Freud. Related: Aggressively; aggressiveness.
aggressor (n.): 1670s, from Latin aggressor, agent noun from aggredi (see aggression).
aggrieve (v.): early 14c., from Old French agrever "make worse; become worse," from Latin aggravare "make heavier" (see aggravation). Related: Aggrieved; aggrieving.
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 agitation). 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," of unknown origin.
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."