actuarial (adj.) Look up actuarial at Dictionary.com
"of the business of an actuary," 1853, from actuary + -al (1). Related: Actuarially.
actuary (n.) Look up actuary at Dictionary.com
1550s, "registrar, clerk," from Medieval Latin actuarius "copyist, account-keeper, short-hand writer," from Latin actus in the specialized sense "public business" (literally "a doing;" see act (n.)). Meaning "person skilled in the calculation of chances and costs," especially as employed by an insurer, is from 1849.
actuate (v.) Look up actuate at Dictionary.com
1590s, "perform" (a sense now obsolete), from Medieval Latin actuatus, past participle of actuare "perform, put into action," from Latin actus "a doing" (see act (n.)). Sense of "put into action, inspire with activity" is from 1640s. Related: Actuated; actuating.
actuation (n.) Look up actuation at Dictionary.com
"a putting in motion, communication of force," 1620s, noun of action from actuate (v.).
acuity (n.) Look up acuity at Dictionary.com
"sharpness, acuteness," early 15c., from Old French acuite (14c.) or directly from Medieval Latin acuitatem (nominative acuitas) "sharpness," noun of state from Latin acuere "to sharpen," literal and figurative (of intellect, emotion, etc.), related to acus "a needle," from PIE root *ak- "rise to a point, be sharp" (see acro-).
aculeate (adj.) Look up aculeate at Dictionary.com
c. 1600, figurative, "pointed, stinging," of writing, from Latin aculeatus "having a sting; thorny, prickly," also figurative, from aculeus "a sting, prickle," diminutive of acus "a needle," from PIE root *ak- "rise to a point, be sharp" (see acro-). From 1660s in a literal sense, in zoology, "furnished with a sting;" 1870 in botany.
acumen (n.) Look up acumen at Dictionary.com
"quickness of perception, keen insight," 1530s, from Latin acumen "a point, sting," hence, figuratively, "mental sharpness, shrewdness," from acuere "to sharpen," literal and figurative (of intellect, emotion, etc.), related to acus "a needle," from PIE root *ak- "rise to a point, be sharp" (see acro-). Related: Acuminous.
acuminate (adj.) Look up acuminate at Dictionary.com
1640s, "having a long, tapering end" (of certain feathers, leaves, etc.), from Latin acuminatus, past participle of acuminare "to sharpen," from acumen "a point" (see acumen). Related: Acuminated; acumination.
acupressure (n.) Look up acupressure at Dictionary.com
1859, name of a method (developed by J.Y. Simpson) of stopping surgical bleeding by pinning or wiring the artery shut, from Latin acus "a needle" (from PIE root *ak- "rise to a point, be sharp;" see acro-) + pressure (n.). From 1958 in reference to the oriental body therapy also known as shiatsu (said to mean literally "Finger-pressure" in Japanese).
acupuncture (n.) Look up acupuncture at Dictionary.com
1680s, "pricking with a needle" as a surgical operation to ease pain, from Latin acus "a needle" (from PIE root *ak- "rise to a point, be sharp;" see acro-) + 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 quickly to a crisis" (opposed to chronic), from Latin acutus "sharp, pointed," figuratively "shrill, penetrating; intelligent, cunning," past participle of acuere "to sharpen" (literal and figurative), from PIE root *ak- "rise to a point, be sharp" (see acro-). Also used of humors (early 15c.). Meaning "ending in a sharp point" is from 1560s; sense of "sharp or penetrating in intellect" is from 1580s. OF feelings, pains, etc., "intense," 1727. As a noun, early 15c. of fevers; c. 1600 as "acute accent." Related: Acutely; acuteness.
ad (n.) Look up ad at Dictionary.com
abbreviation of advertisement, attested by 1841. 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 phrase, "to this, with respect to this, for this (specific purpose)," from ad "to" (see ad-) + hoc, neuter accusative of hic "this." Hence, "appointed or enacted for some particular purpose" (1879).
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). Hence, "to the interests and passions of the person." Originally an argument or appeal to the known preferences or principles of the person addressed, rather than to abstract truth or logic.
ad infinitum Look up ad infinitum at Dictionary.com
"endlessly," Latin, literally "to infinity" from ad "to, unto" (see ad-) + infinitum "infinity," neuter accusative of adjective infinitus "endless" (see infinite). English version to infinity is attested from 1630s.
ad lib Look up ad lib at Dictionary.com
also ad lib., 1811 as a musical instruction, shortened from Latin ad libitum "to (one's) pleasure, as much as one likes" (c. 1600), from ad "to" (see ad-) + libitum "pleasure," accusative of libere "to please" (see libido). As a verb from 1919, as a noun from 1925.
ad nauseam (adv.) 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). Especially of the disgust aroused by wearisome repetition.
ad valorem Look up ad valorem at Dictionary.com
type of customs duties based on the market value of goods at the original place of shipment, 1711, Modern Latin, "(in proportion) to the value," from ad "to" (see ad-) + Late Latin valorem, accusative of valor "value" (see value (n.)). Sometimes abbreviated ad val.
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. Over-correction at the end of the Middle Ages in French and then English "restored" the -d- or a doubled consonant to some words that never had it (accurse, afford). The process went further in England than in France, where the vernacular sometimes resisted the pedantic, resulting in English adjourn, advance, address, advertisement (Modern French ajourner, avancer, adresser, avertissement). In modern word-formation sometimes ad- and ab- are regarded as opposites, but this was not in classical Latin.
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 (16c.), from Latin adagium "adage, proverb," apparently a collateral form of adagio, from ad- "to" (see ad-) + *agi-, root of aio "I say," from PIE *ag- (2) "to speak." But some find this unlikely and suggest the second element might be related to ago "set in motion, drive, urge." Related: Adagial.
adagio (adv.) Look up adagio at Dictionary.com
c. 1746, in music, "slowly, leisurely and gracefully," Italian, a contraction of 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." The name was also used to signify the evil inherent in human nature (as a consequence of Adam's fall), and other qualities (nakedness, gardening) associated with the biblical Adam. Adam's ale "water" is from 1640s. To not know (someone) from Adam "not know him at all" is first recorded 1784. The pet form of the name in Middle English was Addy, hence Addison.
Adam's apple (n.) Look up Adam's apple at Dictionary.com
bulge in the throat caused by the cartilage of the larynx, 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 have been an apple) that Eve gave Adam stuck in his throat. It is more prominent in men than women. The term is mentioned 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.
adamant (adj.) Look up adamant at Dictionary.com
late 14c., "hard, unbreakable," from adamant (n.). Figurative sense of "unshakeable" first recorded 1670s. Related: Adamantly; adamance.
adamant (n.) Look up adamant at Dictionary.com
Old English aðamans "a very hard stone;" the modern word is a mid-14c. borrowing of Old French adamant "diamond; magnet" or directly from Latin adamantem (nominative adamas) "adamant, hardest iron, steel," also used figuratively, of character, from Greek adamas (genitive adamantos), name of a hypothetical hardest material, noun use of an adjective meaning "unbreakable, inflexible," which was metaphoric of anything unalterable (such as Hades), a word of uncertain origin. It is perhaps literally "invincible," from a- "not" (see a- (3)) + daman "to conquer, to tame," from PIE root *deme- "to constrain, force, break (horses)" (see tame (adj.)); or else a word of foreign origin altered to conform to Greek.

Applied in antiquity to a metal resembling gold (Plato), white sapphire (Pliny), magnet (Ovid, perhaps through confusion with Latin adamare "to love passionately"), steel, emery stone, and especially diamond, which is a variant of this word. "The name has thus always been of indefinite and fluctuating sense" [Century Dictionary].
adamantine (adj.) Look up adamantine at Dictionary.com
"made of adamant; having the qualities of adamant" (hard, unyielding, unbreakable, inflexible), c. 1200, from Latin adamantinus "hard as steel, inflexible," from Greek adamantinos "hard as adamant," from adamas (genitive adamantos) "unbreakable, inflexible," as a noun, "hardest material" (see adamant (n.)).
Adamite (n.) Look up Adamite at Dictionary.com
"human being, descendant of Adam" the Biblical first man, 1630s, from Adam + -ite (1). Used from 1620s in reference to perfectionist sects or groups that practice nudism (or, as a 1657 poem has it, "Cast off their petticoats and breeches"), recalling the state of Adam before the Fall. They sprang up 2c. in North Africa, 14c.-15c. in central Europe, and occasionally elsewhere since. Related: Adamic; Adamitic; Adamitism.
adapt (v.) Look up adapt at Dictionary.com
early 15c. (implied in adapted) "to fit (something, for some purpose)," from Old French adapter (14c.), from Latin adaptare "adjust, fit to," from ad- "to" (see ad-) + aptare "to join," from aptus "fitted" (see apt). Intransitive meaning "to undergo modification so as to fit new circumstances" is from 1956. Related: Adapting.
adaptability (n.) Look up adaptability at Dictionary.com
1660s, from adapt + -ability.
adaptable (adj.) Look up adaptable at Dictionary.com
1800, "capable of being made to fit by alteration," from adapt + -able.
adaptation (n.) Look up adaptation at Dictionary.com
c. 1600, "action of adapting (something to something else)," from French adaptation, from Late Latin adaptationem (nominative adaptatio), noun of action from past participle stem of adaptare "to adjust" (see adapt). Meaning "condition of being adapted, state of being fitted to circumstances or relations" is from 1670s. Sense of "modification of a thing to suit new conditions" is from 1790. Biological sense "variations in a living thing to suit changed conditions" first recorded 1859 in Darwin's writings.
adapter (n.) Look up adapter at Dictionary.com
1801, "one who adapts (something to something else)," agent noun from adapt. From 1808 as "mechanical means of adapting objects so they fit or work together" (originally of chemistry apparatus); electrical engineering sense is by 1907.
adaptive (adj.) Look up adaptive at Dictionary.com
1795, from adapt + -ive. Proper formation is adaptative (1831).
adays (adv.) Look up adays at Dictionary.com
late 14c., "by day; on or in the day or time," with adverbial genitive -s from earlier aday (mid-13c.), prepositional phrase used as an adverb, from a- (2) "on, on each" + day (n.). The genitive ending now is regarded as an accusative plural.
add (v.) Look up add at Dictionary.com
late 14c., "to join or unite (something to something else)," from Latin addere "add to, join, attach, place upon," literal and figurative, from ad- "to" (see ad-) + -dere comb. form meaning "to put, place," from dare "to give," from PIE root *do- "to give" (see date (n.1)). Intransitive meaning "to do sums, do addition" also is from late 14c. Related: Added; adding. To add up is from 1754; in the figurative meaning "make sense," 1942. Adding machine is from 1874.
add-on (n.) Look up add-on at Dictionary.com
"additional component," 1941, from verbal phrase add on; see add (v.) + on (adv.).
added (adj.) Look up added at Dictionary.com
"additional," c. 1600, past participle adjective from add (v.).
addendum (n.) Look up addendum at Dictionary.com
1794, "an appendix to a work; a thing to be added," literally "something added," from Latin addendum, neuter of addendus "that which is to be added," gerundive of addere "add to, join, attach" (see add (v.)). Classical plural form is addenda.
adder (n.) Look up adder at Dictionary.com
Old English (West Saxon) næddre (Mercian nedre, Northumbrian nedra), "a snake; the Serpent in the Garden of Eden," from Proto-Germanic *naethro "a snake" (source also of Old Norse naðra, Middle Dutch nadre, Old High German natra, German Natter, Gothic nadrs), from PIE root *nētr- "snake" (source also of Latin natrix "water snake" (the sense is probably by folk-association with nare "to swim"); Old Irish nathir, Welsh neidr "snake, serpent").

Since Middle English restricted to use as the common name of the viper, the only poisonous British reptile (not generally fatal to humans), then by extension applied to venomous or similar snakes elsewhere (puff-adder, etc.). The modern form represents a faulty separation 14c.-16c. of a nadder into an adder, for which see also apron, auger, nickname, orange, humble pie, aitchbone, umpire. Nedder is still a northern English dialect form. Folklore connection with deafness is via Psalms lviii.1-5. The adder is said to stop up its ears to avoid hearing the snake charmer called in to drive it away.
addict (v.) Look up addict at Dictionary.com
1530s (implied in addicted) "to devote or give up (oneself) to a habit or occupation," from Latin addictus, past participle of addicere "to deliver, award, yield; make over, sell," properly "give one's assent to," figuratively "to devote, consecrate; sacrifice, sell out, betray, abandon," from ad- "to" (see ad-) + dicere, which was usually "to say, declare" (see diction), but also "adjudge, allot." "It is a yielding to impulse, and generally a bad one" [Century Dictionary]. Related: Addicted; addicting.
addict (n.) Look up addict at Dictionary.com
"one given over to some practice," 1909, first in reference to morphine, from addict (v.).
addicted (adj.) Look up addicted at Dictionary.com
1530s, "delivered over" by judicial sentence (as a debtor to his creditors, a sense from Roman law); past participle adjective from addict (v.). Sense of "dependent" (1560s) is reflexive, "self-addicted," from the notion of "give over or award (oneself) to someone or some practice;" specialization to narcotics dependency is from c. 1910. Earlier English adjective was simply addict "delivered, devoted" (1520s).
addiction (n.) Look up addiction at Dictionary.com
c. 1600, "tendency, inclination, penchant" (a less severe sense now obsolete); 1640s as "state of being (self)-addicted" to a habit, pursuit, etc., from Latin addictionem (nominative addictio) "an awarding, a delivering up," noun of action from past participle stem of addicere "to deliver, award; devote, consecrate, sacrifice" (see addict (v.)). In the sense "compulsion and need to take a drug as a result of prior use of it" from 1906, in reference to opium (there is an isolated instance from 1779 with reference to tobacco).
addictive (adj.) Look up addictive at Dictionary.com
1815, a word in chemistry and medicine; 1939 in the narcotics sense, from addict (v.) + -ive. Related: Addictively; addictiveness.
additament (n.) Look up additament at Dictionary.com
c. 1400, "anything added, an increase or increment," from Latin additamentum "an increase," from past participle stem of addere "to add" (see add).
addition (n.) Look up addition at Dictionary.com
late 14c., "action of adding numbers;" c. 1400, "that which is added," from Old French adition "increase, augmentation" (13c.), from Latin additionem (nominative additio) "an adding to, addition," noun of action from past participle stem of addere "add to, join, attach" (see add). Phrase in addition to "also" is from 1680s.
additional (adj.) Look up additional at Dictionary.com
1640s, "added, supplementary," from addition + -al (1). Related: Additionally.
additive (n.) Look up additive at Dictionary.com
"something that is added" to a chemical solution or food product, 1945, from additive (adj.).