Online Etymology Dictionary

acrostic (n.): short poem in which the initial letters of the lines, taken in order, spell a word or phrase, 1580s, from Medieval Latin acrostichis, from Greek akrostikhis, from akros "at the end, outermost" (see acrid) + stikhos "line of verse," literally "row" (see stair).
acrylic (adj.): 1855, "of or containing acryl," name of a radical from acrolein (1843), the name of a liquid in onions and garlic that makes eyes tear, from Latin acer "sharp" (see acrid) + olere "to smell" (see odor) + -in (see -ine (2)). With adjectival suffix + -ic. Modern senses often short for acrylic fiber, acrylic resin, etc.
act (n.): late 14c., "a thing done," from Old French acte "(official) document," and directly from Latin actus "a doing, a driving, impulse; a part in a play, act," and actum "a thing done," originally a legal term, both from agere "to do, set in motion, drive, urge, chase, stir up," from PIE root *ag- "to drive, draw out or forth, move" (cf. Greek agein "to lead, guide, drive, carry off," agon "assembly, contest in the games," agogos "leader;" Sanskrit ajati "drives," ajirah "moving, active;" Old Norse aka "to drive;" Middle Irish ag "battle").

Theatrical ("part of a play," 1510s) and legislative (early 15c.) senses of the word also were in Latin. Meaning "display of exaggerated behavior" is from 1928. In the act "in the process" is from 1590s, perhaps originally from the 16c. sense of the act as "sexual intercourse." Act of God "uncontrollable natural force" recorded by 1726.
An act of God is an accident which arises from a cause which operates without interference or aid from man (1 Pars. on Cont. 635); the loss arising wherefrom cannot be guarded against by the ordinary exertions of human skill and prudence so as to prevent its effect. [William Wait, "General Principles of the Law," Albany, 1879]
act (v.): mid-15c., "to act upon or adjudicate" a legal case; 1590s in the theatrical sense, from Latin actus, past participle of agere (see act (n.)). To act up "be unruly" is from 1903. To act out "behave anti-socially" (1974) is from psychiatric sense of "expressing one's unconscious impulses or desires." Related: Acted; acting.
Actaeon: in Greek mythology, the name of the hunter who discovered Artemis bathing and was changed by her to a stag and torn to death by his hounds. The name is of unknown origin. Sometimes used figuratively in 17c. for "a cuckold" (because of his "horns").
acting (adj.): 1590s, "putting forth activity," present participle adjective from act (v.). Meaning "performing temporary duties" is from 1797.
acting (n.): c.1600, "performance of deeds;" 1660s, "performance of plays;" verbal noun from present participle of act (v.). Acting out in psychology is from 1945.
actinium (n.): radioactive element discovered in 1899, from Greek actin-, comb. form of aktis (genitive aktinos) "ray, radiance" (see actino-) + chemical suffix -ium.
actino-: before vowels actin-, word-forming element meaning "pertaining to rays," from Greek aktis (genitive aktinos) "ray, radiance;" perhaps cognate with Sanskrit aktuh "light, ray," Gothic uhtwo "dawn, daybreak," Lithuanian anksti "early."
action (n.): mid-14c., "cause or grounds for a lawsuit," from Anglo-French accioun, Old French accion (12c.) "action, lawsuit, case," from Latin actionem (nominative actio) "a putting in motion; a performing, doing," noun of action from past participle stem of agere "to do" (see act (v.)). Sense of "something done, an act, deed" is late 14c. Meaning "fighting" is from c.1600. As a film director's command, it is attested from 1923. Meaning "excitement" is recorded from 1968. Phrase actions speak louder than words is attested from 1731.
actionable (adj.): 1590s; from action + -able.
activate (v.): 1620s; see active + -ate (2). Related: Activated; activating.
activation (n.): 1906, noun of action from activate (v.).
active (adj.): mid-14c., "given to worldly activity" (opposed to contemplative or monastic), from Old French actif (12c.) or directly from Latin activus, from actus (see act (n.)). As "capable of acting" (opposed to passive), from late 14c. Meaning "energetic, lively" is from 1590s; that of "working, effective, in operation" is from 1640s. Active voice is recorded from 1765 (grammatical use of active dates from mid-15c.).
actively (adv.): c.1400, "secularly," from active + -ly (2). Meaning "vigorously" is early 15c.
activism (n.): 1920 in the political sense; see activist + -ism. Earlier (1907) it was used in reference to a philosophical theory.
activist (n.): "one who advocates a doctrine of direct action," 1915; from active + -ist. Originally in reference to political forces in Sweden advocating abandonment of neutrality in World War I and active support for the Central Powers.
activities (n.): in schoolwork sense, 1923, American English, from activity.
activity (n.): c.1400, "active or secular life," from Old French activité, from Medieval Latin activitatem (nominative activitas), a word in Scholastic philosophy, from Latin activus (see active). Meaning "state of being active, briskness, liveliness" recorded from 1520s; that of "capacity for acting on matter" is from 1540s.
actor (n.): late 14c., "an overseer, guardian, steward," from Latin actor "an agent or doer," also "theatrical player," from past participle stem of agere (see act (n.)). Mid-15c. as "a doer, maker," also "a plaintiff." Sense of "one who performs in plays" is 1580s, originally applied to both men and women.
actress (n.): 1580s, "female who does something;" see actor + -ess; stage sense is from 1700. Sometimes French actrice was used.
Acts: short for "Acts of the Apostles" in New Testament, from 1530s.
actual (adj.): early 14c., "pertaining to an action," from Old French actuel "now existing, up to date" (13c.), from Late Latin actualis "active, pertaining to action," adjectival form of Latin actus (see act (n.)). The broader sense of "real, existing" (as opposed to potential, ideal, etc.) is from late 14c.
actuality (n.): late 14c., "power, efficacy," from Old French actualite and directly from Medieval Latin actualitatem (nominative actualitas), from Late Latin actualis (see actual). A Latin loan-translation of Greek energeia. Meaning "state of being real" is from 1670s (actualities "existing conditions" is from 1660s).
Mod. use of actuality in the sense of realism, contact with the contemporary, is due to Fr. actualité, from actuel, which does not mean actual, real, but now existing, up to date. [Weekley]
actualization (n.): 1824, noun of action from actualize.
actualize (v.): 1810, first attested in Coleridge, from actual + -ize. Related: Actualized; actualizing.
actually (adv.): early 15c., "in fact, in reality" (as opposed to in possibility), from actual + -ly (2). Meaning "actively, vigorously" is from mid-15c.; that of "at this time, at present" is from 1660s. As an intensive added to a statement and suggesting "as a matter of fact, really, in truth" it is attested from 1762.
actuarial (adj.): 1869, from actuary + -al (1). Related: Actuarially.
actuary (n.): 1550s, "registrar, clerk," from Latin actuarius "copyist, account-keeper," from actus "public business" (see act (n.)). Modern insurance office meaning first recorded 1849.
actuate (v.): 1590s, from Medieval Latin actuatus, past participle of actuare, from Latin actus (see act (n.)). Related: Actuated; actuating.
acuity (n.): early 15c., from Middle French acuité (16c.) or directly from Medieval Latin acuitatem (nominative acuitas) "sharpness," from Latin acuere "to sharpen," related to acus "needle," acuere "to sharpen," from PIE root *ak- "rise to a point, be sharp" (see acrid).
acumen (n.): 1530s, from Latin acumen "a point, sting," hence "mental sharpness, shrewdness," from acuere "to sharpen" (see acuity).
acupressure (n.): 1859, from Latin acus "needle" (see acuity) + pressure (n.).
acupuncture (n.): 1680s, "pricking with a needle" to ease pain, from Latin acus "needle" (see acuity) + puncture. The verb is first recorded 1972.
acupuncturist (n.): 1843, from acupuncture + -ist.
acute (adj.): late 14c., originally of fevers and diseases, "coming and going quickly" (opposed to a chronic), from Latin acutus "sharp, pointed," figuratively "shrill, penetrating; intelligent, cunning," past participle of acuere "sharpen" (see acuity). Meaning "sharp, irritating" is from early 15c. Meaning "intense" is from 1727. Related: Acutely; acuteness.
ad (n.): 1841, shortened form of advertisement. Long resisted by those in the trade, and denounced 1918 by the president of a national advertising association as "the language of bootblacks, ... beneath the dignity of men of the advertising profession."
ad hoc: Latin, literally "for this (specific purpose)."
ad hominem: c.1600, Latin, literally "to a man," from ad "to" (see ad-) + hominem, accusative of homo "man" (see homo- (2)).
ad infinitum: Latin, literally "to infinity" from infinitum "infinity," neuter of adjective infinitus "endless" (see infinite).
ad lib: 1811, shortened from Latin ad libitum "at one's pleasure, as much as one likes" (c.1600), from libere "to please" (see libido). First recorded as one word 1919 (v.), 1925 (n.).
ad nauseam: "to a sickening extent," Latin, literally "to sickness" (see nausea).
ad valorem: type of customs duties, 1711, Latin, "in proportion to the value" (see value).
ad-: prefix expressing direction toward or in addition to, from Latin ad "to, toward" in space or time; "with regard to, in relation to," as a prefix, sometimes merely emphatic, from PIE *ad- "to, near, at" (cognate with Old English æt; see at). Simplified to a- before sc-, sp- and st-; modified to ac- before many consonants and then re-spelled af-, ag-, al-, etc., in conformity with the following consonant (e.g. affection, aggression). In Old French, reduced to a- in all cases (an evolution already underway in Merovingian Latin), but written forms were refashioned after Latin in 14c. in French and 15c. in English words picked up from Old French. In many cases pronunciation followed the shift.
Ada: fem. proper name, from Hebrew Adha, literally "ornament."
adage (n.): 1540s, Middle French adage, from Latin adagium "adage, proverb," apparently from adagio, from ad- "to" (see ad-) + *agi-, root of aio "I say," from PIE *ag- "to speak." But Tucker thinks the second element is rather ago "set in motion, drive, urge."
adagio (adv.): c.1746, "slowly, leisurely," Italian, from ad agio, from ad "to, at" (see ad-) + agio "leisure," from Vulgar Latin adjacens, present participle of adjacere "to lie at, to lie near" (cf. adjacent). In musical sense of "a slow movement" (n.), first attested 1784.
Adam: masc. proper name, Biblical name of the first man, from Hebrew adam "man," literally "(the one formed from the) ground" (Hebrew adamah "ground"); cf. Latin homo "man," humanus "human," humus "earth, ground, soil." To not know (someone) from Adam "not know him at all" is first recorded 1784.
Adam's apple: 1755, perhaps an inexact translation of Hebrew tappuah haadam, literally "man's swelling," from ha-adam "the man" + tappuah "anything swollen." The reference is to the legend that a piece of the forbidden fruit (commonly believed to be an apple) that Eve gave Adam stuck in his throat. The term is mentioned in early 15c. as the name of some actual oriental fruit.
adamant (adj.): late 14c., "hard, unbreakable," from adamant (n.). Figurative sense of "unshakeable" first recorded 1670s. Related: Adamantly; adamance.