across (adv.) Look up across at Dictionary.com
early 14c., acros, earlier a-croiz (c.1300), from Anglo-French an cros "in a crossed position," literally "on cross" (see cross (n.)). Prepositional meaning "from one side to another" is first recorded 1590s; meaning "on the other side (as a result of crossing)" is from 1750. Phrase across the board originally is from horse-racing, in reference to a bet of the same amount of money on a horse to win, place, or show.
acrostic (n.) Look up acrostic at Dictionary.com
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.) Look up acrylic at Dictionary.com
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.) Look up act at Dictionary.com
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" (cognates: 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.) Look up act at Dictionary.com
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 Look up Actaeon at Dictionary.com
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.) Look up acting at Dictionary.com
1590s, "putting forth activity," present participle adjective from act (v.). Meaning "performing temporary duties" is from 1797.
acting (n.) Look up acting at Dictionary.com
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.) Look up actinium at Dictionary.com
radioactive element discovered in 1899, from Greek actin-, comb. form of aktis (genitive aktinos) "ray, radiance" (see actino-) + chemical suffix -ium.
actino- Look up actino- at Dictionary.com
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.) Look up action at Dictionary.com
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.) Look up actionable at Dictionary.com
1590s; from action + -able.
activate (v.) Look up activate at Dictionary.com
1620s; see active + -ate (2). Related: Activated; activating.
activation (n.) Look up activation at Dictionary.com
1906, noun of action from activate (v.).
active (adj.) Look up active at Dictionary.com
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.) Look up actively at Dictionary.com
c.1400, "secularly," from active + -ly (2). Meaning "vigorously" is early 15c.
activism (n.) Look up activism at Dictionary.com
1920 in the political sense; see activist + -ism. Earlier (1907) it was used in reference to a philosophical theory.
activist (n.) Look up activist at Dictionary.com
"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.) Look up activities at Dictionary.com
in schoolwork sense, 1923, American English, from activity.
activity (n.) Look up activity at Dictionary.com
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.) Look up actor at Dictionary.com
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.) Look up actress at Dictionary.com
1580s, "female who does something;" see actor + -ess; stage sense is from 1700. Sometimes French actrice was used.
Acts Look up Acts at Dictionary.com
short for "Acts of the Apostles" in New Testament, from 1530s.
actual (adj.) Look up actual at Dictionary.com
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.) Look up actuality at Dictionary.com
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.) Look up actualization at Dictionary.com
1824, noun of action from actualize.
actualize (v.) Look up actualize at Dictionary.com
1810, first attested in Coleridge, from actual + -ize. Related: Actualized; actualizing.
actually (adv.) Look up actually at Dictionary.com
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.) Look up actuarial at Dictionary.com
1853, from actuary + -al (1). Related: Actuarially.
actuary (n.) Look up actuary at Dictionary.com
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.) Look up actuate at Dictionary.com
1590s, from Medieval Latin actuatus, past participle of actuare, from Latin actus (see act (n.)). Related: Actuated; actuating.
acuity (n.) Look up acuity at Dictionary.com
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.) Look up acumen at Dictionary.com
1530s, from Latin acumen "a point, sting," hence "mental sharpness, shrewdness," from acuere "to sharpen" (see acuity).
acupressure (n.) Look up acupressure at Dictionary.com
1859, from Latin acus "needle" (see acuity) + pressure (n.).
acupuncture (n.) Look up acupuncture at Dictionary.com
1680s, "pricking with a needle" to ease pain, from Latin acus "needle" (see acuity) + puncture. The verb is first recorded 1972.
acupuncturist (n.) Look up acupuncturist at Dictionary.com
1843, from acupuncture + -ist.
acute (adj.) Look up acute at Dictionary.com
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.) Look up ad at Dictionary.com
1841, shortened form of advertisement. Long resisted by those in the trade, and according to Mencken (1945) denounced by William C. D'Arcy (president of Associated Advertising Clubs of the World) as "the language of bootblacks, ... beneath the dignity of men of the advertising profession."
ad hoc Look up ad hoc at Dictionary.com
Latin, literally "for this (specific purpose)."
ad hominem Look up ad hominem at Dictionary.com
c.1600, Latin, literally "to a man," from ad "to" (see ad-) + hominem, accusative of homo "man" (see homunculus).
ad infinitum Look up ad infinitum at Dictionary.com
Latin, literally "to infinity" from ad "to" (see ad-) + infinitum "infinity," neuter of adjective infinitus "endless" (see infinite).
ad lib Look up ad lib at Dictionary.com
1811, shortened from Latin ad libitum "at one's pleasure, as much as one likes" (c.1600), from ad "to" (see ad-) + libitum, accusative of libere "to please" (see libido). First recorded as one word 1919 (v.), 1925 (n.).
ad nauseam Look up ad nauseam at Dictionary.com
"to a sickening extent," Latin, literally "to sickness," from ad "to" (see ad-) + nauseam, accusative of nausea (see nausea).
ad valorem Look up ad valorem at Dictionary.com
type of customs duties, 1711, Modern Latin, "(in proportion) to the value," from ad "to" (see ad-) + Late Latin valorem, accusative of valor "value" (see value (n.)).
ad- Look up ad- at Dictionary.com
word-forming element 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 (as in affection, aggression). In Old French, reduced to a- in all cases (an evolution already underway in Merovingian Latin), but written forms in French were refashioned after Latin in 14c. and English did likewise 15c. in words it had picked up from Old French. In many cases pronunciation followed the shift.
Ada Look up Ada at Dictionary.com
fem. proper name, from Hebrew Adha, literally "ornament."
adage (n.) Look up adage at Dictionary.com
"brief, familiar proverb," 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.) Look up adagio at Dictionary.com
c.1746, in music, "slowly, leisurely and gracefully," Italian, from ad agio, from ad "to, at" (see ad-) + agio "leisure," from Vulgar Latin adiacens, present participle of adiacere "to lie at, to lie near" (compare adjacent). In noun sense of "a slow movement," first attested 1784.
Adam Look up Adam at Dictionary.com
masc. proper name, Biblical name of the first man, progenitor of the human race, from Hebrew adam "man," literally "(the one formed from the) ground" (Hebrew adamah "ground"); compare 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 (n.) Look up Adam's apple at Dictionary.com
1731, corresponding to Latin pomum Adami, 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 an actual oriental and Mediterranean fruit, a variety of lime with an indentation fancied to resemble the marks of Adam's teeth.