Arctic Circle Look up Arctic Circle at Dictionary.com
1550s, in reference to a celestial circle, a line around the sky which, in any location, bounds the stars which are ever-visible from that latitude (in the Northern Hemisphere, this is focused on the celestial north pole); the concept goes back to the ancient Greeks, for whom this set of constellations included most prominently the two bears (arktoi), hence the name for the circle (see arctic). Of Earth, the circle 66 degrees 32 minutes north of the equator, marking the southern extremity of the polar day, it is recorded from 1620s.
Arcturus Look up Arcturus at Dictionary.com
late 14c., bright star in the constellation Bootes (also used of the whole constellation), from Latin Arcturus, from Greek Arktouros; anciently associated with the Bear, and its name is Greek for "guardian of the bear." See arctic; second element is from ouros "watcher, guardian, ward," from PIE root *wer- (4) "perceive" (see ward (n.)).

Arcturus in the Bible (Job ix.9 and xxxviii.32) is a mistranslation by Jerome (continued in KJV) of Hebrew 'Ayish, which refers to what we see as the "bowl" of the Big Dipper. In Israel and Arabia, the seven stars of the Great Bear seem to have been a bier (the "bowl") followed by three mourners. In the Septuagint it was translated as Pleiada, which is equally incorrect. The double nature of the great bear/wagon (see Big Dipper) has given two different names to the constellation that follows it: Arktouros "bear-ward" and bootes "the wagoner."
arcuate (adj.) Look up arcuate at Dictionary.com
"bent like a bow," 1620s, from Latin arcuatus "bow-like, arched," past participle of arcuare "to bend like a bow," from arcus "bow" (see arc (n.)).
ardency (n.) Look up ardency at Dictionary.com
1540s, "warmth of feeling, desire," from ardent + -cy. A figurative sense, the literal meaning "intensity of heat" wasn't attested in English until 1630s.
ardent (adj.) Look up ardent at Dictionary.com
early 14c., of alcoholic distillates, brandy (ardent spirits), etc., from Old French ardant (13c.) "burning, hot; zealous," from Latin ardentem (nominative ardens) "glowing, fiery, hot, ablaze," also used figuratively of passions, present participle of ardere "to burn," from PIE root *as- "to burn, glow" (source also of Old English æsce "ashes;" see ash (n.1)).

Ardent spirits (late 15c.) so called because they are inflammable, but the term now, if used at all, probably is felt in the figurative sense. The figurative sense (of "burning with" passions, desire, etc.) is from late 14c.; literal sense of "burning, parching" (c. 1400) remains rare. Related: Ardently.
ardor (n.) Look up ardor at Dictionary.com
early 15c., "heat of passion or desire," from Old French ardure "heat, glow; passion" (12c.), from Latin ardorem (nominative ardor) "a flame, fire, burning, heat;" also of feelings, etc., "eagerness, zeal," from ardere "to burn" (see ardent). In Middle English, used of base passions; since Milton's time, of noble ones.
ardour (n.) Look up ardour at Dictionary.com
chiefly British English spelling of ardor (q.v.); for spelling, see -or.
arduous (adj.) Look up arduous at Dictionary.com
1530s, "hard to accomplish, difficult to do," from Latin arduus "high, steep," also figuratively, "difficult," from PIE root *eredh- "to grow, high" (see ortho-). Literal sense of "high, steep, difficult to climb," attested in English from 1709.
ardurous (adj.) Look up ardurous at Dictionary.com
"full of ardor," 1770, a variant of arduous with overtones of amorous. Useful only to poets and first attested in Chatterton; perhaps, then, like his works, an instance of faux medievalism.
are (v.) Look up are at Dictionary.com
present plural indicative of be (q.v.), from Old English earun (Mercian), aron (Northumbrian). Also from Old Norse cognates. In 17c., began to replace be, ben as first person plural present indicative in standard English. The only non-dialectal survival of be in this sense is the powers that be. But in southwest England, we be (in Devonshire us be) remains non-standard idiom as a contradictory positive ("You people aren't speaking correct English." "Oh, yes we be!").
are (n.) Look up are at Dictionary.com
square unit of 10 meters on each side, 1819, from French, formed 1795 by decree of the French National Convention, from Latin area "vacant piece of ground" (see area).
area (n.) Look up area at Dictionary.com
1530s, "vacant piece of ground," from Latin area "level ground, open space," used of building sites, playgrounds, threshing floors, etc.; which is of uncertain origin. Perhaps related to arere "to become dry," on notion of a burned clearing or dry, bare space. The generic sense of "amount of surface (whether open or not) contained within any set of limits" is from 1845. Area code in North American telephone systems is attested from 1959.
areal (adj.) Look up areal at Dictionary.com
1670s, from Latin arealis, from area (see area).
aren't Look up aren't at Dictionary.com
1794, contraction of are not, originally written are'n't and generally so into early 19c.
If "ain't I?" is objected to, surely "aren't I?" is very much worse. [Lady Grove, "The Social Fetich," 1907]
arena (n.) Look up arena at Dictionary.com
1620s, "place of combat," from Latin harena "place of combat," originally "sand, sandy place," perhaps from Etruscan. The central stages of Roman amphitheaters were strewn with sand to soak up the blood.
areola (n.) Look up areola at Dictionary.com
"colored circle around a nipple," 1706, from Latin areola, literally "small area," diminutive of area (see area). Introduced in this sense 1605 by Swiss anatomist and botanist Caspar Bauhin (1560-1624).
areolas (n.) Look up areolas at Dictionary.com
nativized plural of areola (q.v.), which has its proper plural in areolae (see -ae).
Areopagite (n.) Look up Areopagite at Dictionary.com
"member of the Areopagus court," late 14c.; see Areopagus + -ite (1). See Acts xvii.34.
Areopagus Look up Areopagus at Dictionary.com
1640s, Greek, Areios pagos "the hill of Ares," west of the Acropolis in Athens, where the highest judicial court sat; second element from pagos "rocky hill." Sense extended to "any important tribunal."
Ares Look up Ares at Dictionary.com
Greek god of war, identified by Romans with their Mars; literally "injurer, destroyer," from are "bane, ruin," perhaps cognate with Sanskrit irasya "ill-will" (see ire).
arete (n.1) Look up arete at Dictionary.com
"sharp crest of a mountain," 1862, from Swiss French arête, from Latin arista "ear of grain, the top of an ear," which probably is of Etruscan origin. The figure is of something jagged.
arete (n.2) Look up arete at Dictionary.com
important concept in Greek philosophy, "virtue, excellence," especially of manly qualities; literally "that which is good." The comparative form is areion, the superlative is aristos (compare aristocracy).
argent (n.) Look up argent at Dictionary.com
c. 1300, "quicksilver, the metal mercury," from Old French argent (11c.), from Latin argentum "silver, silver work, white money," from PIE *arg-ent- (source also of Avestan erezata-, Old Persian ardata-, Armenian arcat, Old Irish argat, Breton arc'hant "silver"), from root *arg- "to shine; white," thus "the shining or white metal, silver" (source also of Greek argos "white," arguron "silver;" Sanskrit arjuna- "white, shining," rajata- "silver," Hittite harki- "white"). Meaning "silver, silver coin" is early 15c. in English; the adjective sense "silver-colored," late 15c.
Argentina Look up Argentina at Dictionary.com
South American nation, from Latin argentinus "of silver" (see argent); a Latinized form of (Rio) de la Plata, from Spanish plata "silver."
argentine (adj.) Look up argentine at Dictionary.com
"silver-colored," mid-15c., from Latin argentinus "of silver," from argentum (see argent).
Argentine (adj.) Look up Argentine at Dictionary.com
"of or from Argentina," 1830 (from 1829 as a noun); Argentinian is from 1845 as a noun; 1858 as an adjective.
Argive (adj.) Look up Argive at Dictionary.com
"of Argos," hence, especially in Homeric usage, "the Greeks," as a byword for Achaean (he describes Agamemnon as king of Argos), 1520s, from Latin Argivus, from Greek Argeios "of Argos."
argle (v.) Look up argle at Dictionary.com
1580s "to argue obstinately," from argue, perhaps by influence of haggle. Reduplicated form argle-bargle (sometimes argy-bargy) "wrangling" is attested from 1872.
Argo Look up Argo at Dictionary.com
name of the ship in which Jason and his companions sought the Fleece in Colchis, in Greek, literally "The Swift," from argos "swift" (adj.), an epithet, literally "shining, bright" (see argent; compare also Sanskrit cognate rjrah "shining, glowing, bright," also "swift"), "because all swift motion causes a kind of glancing or flickering light" [Liddell & Scott].
argon (n.) Look up argon at Dictionary.com
chemical element, 1894, Modern Latin, from Greek argon, neuter of argos "lazy, idle, not working the ground, living without labor," from a- "without" (see a- (3)) + ergon "work" (see organ). So called by its discoverers, Baron Rayleigh and Sir William Ramsay, for its inert qualities.
Argonaut (n.) Look up Argonaut at Dictionary.com
"sailor of the Argo," 1580s (implied in argonautic), from Argo + Greek nautes "sailor" (see naval). Adventurers in the California Gold Rush of 1848 were called argonauts (because they sought the golden fleece) by those who stayed home.
argosy (n.) Look up argosy at Dictionary.com
1570s, from Italian (nave) Ragusea "(vessel) of Ragusa," maritime city on the Dalmatian coast of the Adriatic (modern Dubrovnik in Croatia). Their large merchant ships brought rich Eastern goods to 16c. England. The city name sometimes was Aragouse or Arragosa in 16c. English.
argot (n.) Look up argot at Dictionary.com
1860, from French argot (17c.) "the jargon of Paris rogues and thieves," earlier "the company of beggars," from Middle French argot, "group of beggars," origin unknown. Gamillscheg suggests a connection to Old French argoter "to cut off the stubs left in pruning," with a connecting sense of "to get a grip on." The best English equivalent is perhaps cant. The German equivalent is Rotwelsch, literally "Red Welsh," but the first element may be connected with Middle High German rot "beggar." Earlier in English was pedlar's French (1520s) "language of thieves and vagabonds."
arguable (adj.) Look up arguable at Dictionary.com
1610s, from argue + -able.
arguably (adv.) Look up arguably at Dictionary.com
"as may be shown by argument," 1890, from arguable + -ly (2).
argue (v.) Look up argue at Dictionary.com
c. 1300, "to make reasoned statements to prove or refute a proposition," from Old French arguer "maintain an opinion or view; harry, reproach, accuse, blame" (12c.), from Latin argutare "to prattle, prate," frequentative of arguere "make clear, make known, prove, declare, demonstrate," from PIE *argu-yo-, from root *arg- "to shine, be white, bright, clear" (see argent). Meaning "to oppose, dispute" is from late 14c. Related: Argued; arguing.
arguendo Look up arguendo at Dictionary.com
"in the course of argument," 1817, courtroom Latin, from Medieval Latin ablative of arguendum, gerundive of arguere "to argue" (see argue).
arguer (n.) Look up arguer at Dictionary.com
late 14c., agent noun from argue (v.).
argufy (v.) Look up argufy at Dictionary.com
1751, colloquial, from argue + -fy.
argument (n.) Look up argument at Dictionary.com
early 14c., "statements and reasoning in support of a proposition," from Old French arguement "reasoning, opinion; accusation, charge" (13c.), from Latin argumentum "evidence, ground, support, proof; a logical argument," from arguere "to argue" (see argue). Sense passed through "subject of contention" to "a quarrel," a sense formerly attached to argumentation.
argumentation (n.) Look up argumentation at Dictionary.com
mid-15c., "presentation of formal arguments," from Old French argumentacion (14c.), from Latin argumentationem (nominative argumentatio) "the bringing forth of a proof," noun of action from past participle stem of argumentari (see argue). Meaning "debate, wrangling, argument back and forth" is from 1530s.
argumentative (adj.) Look up argumentative at Dictionary.com
mid-15c., "pertaining to arguments," from Old French argumentatif or directly from Latin argumentat-, past participle stem of argumentari (see argue) + -ive. Meaning "fond of arguing" is recorded from 1660s. Related: Argumentatively; argumentativeness.
Argus Look up Argus at Dictionary.com
hundred-eyed giant of Greek mythology, late 14c., from Latin, from Greek Argos, literally "the bright one," from argos "shining, bright" (see argent). His epithet was Panoptes "all-eyes." After his death, Hera transferred his eyes to the peacock's tail. Used in figurative sense of "very vigilant person."
Argyle (n.) Look up Argyle at Dictionary.com
"diamond-shaped pattern of two or more colors in fabric," said to be so called from similarity to tartans worn by Campbell clan of Argyll, Scotland. The place name is literally "land of the Gaels," from Old Irish airer "country." Argyle socks is from 1935.
aria (n.) Look up aria at Dictionary.com
from Italian aria, literally "air" (see air (n.1)).
Arian (adj.) Look up Arian at Dictionary.com
1530s, pertaining to the doctrines of Arius, priest in Alexandria early 4c., who posed the question of Christ's nature in terms which appeared to debase the Savior's relation to God (denial of consubstantiation). Besides taking an abstract view of Christ's nature, he reaffirmed man's capacity for perfection. The dissention was widespread and split the Church for about a century during a crucial time.
Arianism (n.) Look up Arianism at Dictionary.com
c. 1600, from Arian + -ism.
arid (adj.) Look up arid at Dictionary.com
1650s, "dry, parched," from French aride (15c.) or directly from Latin aridus "dry, arid, parched," from arere "to be dry," from PIE root *as- "to burn, glow" (see ash (n.1)). Figurative sense of "uninteresting" is from 1827. Related: Aridly.
aridity (n.) Look up aridity at Dictionary.com
1590s, from Middle French aridité or directly from Latin ariditatem (nominative ariditas) "dryness," from aridus (see arid). The Latin word was used figuratively of unadorned styles as well as stingy men.
ariel Look up ariel at Dictionary.com
1382, in the Wyclif Bible, a word taken untranslated from the Vulgate, from Greek ariel (Sept.), from Hebrew ariel; in later Bibles, translated as "altar."
(Gesenius would here translate "fire-hearth of God," after Arab. arr; elsewhere in O.T. the same word occurs as a man's name, and appellation of Jerusalem, where it is taken as = "lion of God.") Ariel in T. Heywood and Milton is the name of an angel, in Shakespeare of "an Ayrie spirit"; in Astron. of one of the satellites of Uranus. [OED]
As the name of a species of gazelle found in the Middle East, 1832, from Arabic aryil, variant of ayyil "stag."