aquaculture (n.) Look up aquaculture at Dictionary.com
1869, from aqua- + culture (n.).
aqualung (n.) Look up aqualung at Dictionary.com
1950, from aqua- + lung. Developed 1943 by Jacques Cousteau and Emile Gagnan.
aquamarine (n.) Look up aquamarine at Dictionary.com
1590s, agmarine, "bluish-green type of beryl," from French or Provençal, from Latin aqua marina "sea water," from aqua "water" (see aqua-) + marina, fem. of marinus "of the sea" (see marine (adj.)). Apparently first used as a description of a bluish-green color by John Ruskin, 1846. Abbreviation aqua is attested from 1936.
aquanaut (n.) Look up aquanaut at Dictionary.com
1881, from aqua- + ending from Greek nautes "sailor" (see naval).
aquarelle (n.) Look up aquarelle at Dictionary.com
1855, from French aquarelle (18c.), from Italian acquerella "water-color," diminutive of acqua, from Latin aqua "water" (see aqua-).
Aquarian (adj.) Look up Aquarian at Dictionary.com
1940, in the astrological/New Age sense; see Aquarius + -ian.
aquarium (n.) Look up aquarium at Dictionary.com
1830, noun use of neuter of Latin aquarius "pertaining to water," as a noun, "water-carrier," genitive of aqua "water" (see aqua-). The word existed in Latin, but there it meant "drinking place for cattle." Originally especially for growing aquatic plants; An earlier attempt at a name for "fish tank" was marine vivarium.
Aquarius Look up Aquarius at Dictionary.com
faint constellation and 11th zodiac sign, late Old English, from Latin aquarius, literally "water carrier," properly an adjective, "pertaining to water" (see aquarium); a loan-translation of Greek Hydrokhoos "the water-pourer," old Greek name of this constellation.

Aquarians were a former Christian sect that used water instead of wine at the Lord's Supper. Age of Aquarius (1940) is an astrological epoch supposed to have begun in the 1960s, embodying the traits of this sign and characterized by world peace and human brotherhood. The term and the concept probably got a boost in popular use when An Aquarian Exposition was used as the sub-name of the Woodstock Music & Art Fair (1969).
aquatic (adj.) Look up aquatic at Dictionary.com
late 15c., from Middle French and Old French aquatique (13c.), from Latin aquaticus "growing in water; bringing rain," from aqua "water" (see aqua-)
aquatint (n.) Look up aquatint at Dictionary.com
1782, "engraving made with aqua fortis," from Italian acquatinta, from Latin aqua tincta "dyed water;" see aqua- + tinct.
aqueduct (n.) Look up aqueduct at Dictionary.com
1530s, from Latin aquaeductus "conveyance of water," from aquae, genitive of aqua "water" (see aqua-), + ductus "a leading, conducting," past participle of ducere "to lead" (see duke (n.)).
aqueous (adj.) Look up aqueous at Dictionary.com
1640s, from Latin aqua "water" (see aqua-) on analogy of French aqueux "watery" (16c., which, however, is from Late Latin aquosus "abounding in water"). Or by analogy of Latin terreus "earthy," from terra "earth." Aqueous humor is the original use in English.
aquifer (n.) Look up aquifer at Dictionary.com
1897, coined from Latin aqui-, comb. form of aqua "water" (see aqua-) + -fer "bearing," from ferre "to bear, carry" (see infer).
aquiline (adj.) Look up aquiline at Dictionary.com
"curved like an eagle's beak," 1640s, originally in English in reference to long, hooked noses, from Latin aquilinus "of or like an eagle," from aquila "eagle," a word of uncertain origin, usually explained as "the dark bird;" compare aquilus "blackish, swarthy, of the color of darkness," but some suggest the color word is from the bird.

De Vaan writes, "It is possible that 'eagle' was derived from aquilus 'dark' when this had received its colour meaning. It may not be the only dark bird, but it is certainly one of the biggest and most majestic of them." As for aquilus, "The Romans derives this colour from aqua 'water', which [Etymologicum Magnum] reject because they cannot imagine water being black. Still, this seems a more likely derivation to me than from aquila 'eagle', as assumed by Cohen 2004: 32."
aquiver (adv.) Look up aquiver at Dictionary.com
1864, from a- (1) + quiver (v.).
Arab (n.) Look up Arab at Dictionary.com
late 14c. (Arabes, a plural form), from Old French Arabi, from Latin Arabs (accusative Arabem), from Greek Araps (genitive Arabos), from Arabic 'arab, indigenous name of the people, perhaps literally "inhabitant of the desert" and related to Hebrew arabha "desert." Meaning "homeless little wanderer, child of the street" is from 1848 (originally Arab of the city), in reference to nomadic ways. Arab League formed in Cairo, March 22, 1945.
arabesque (n.) Look up arabesque at Dictionary.com
1610s, "Moorish or Arabic ornamental design," from French arabesque (16c.), from Italian arabesco, from Arabo "Arab," with reference to Moorish architecture. As a ballet pose, first attested 1830. Musical sense, in reference to an ornamented theme, is from 1864, originally the title given by Robert Schumann to one of his piano pieces.
Arabia Look up Arabia at Dictionary.com
1711; see Arab + -ia. The older name for "the country of Arabia" was Araby (late 13c.).
Arabian Look up Arabian at Dictionary.com
c. 1300, adjective and noun; see Arab + -ian. As a prized type of horse, it is attested from 1660s. The Arabian bird was the phoenix.
Arabic (adj.) Look up Arabic at Dictionary.com
early 14c., from Old French Arabique (13c.), from Latin Arabicus "Arabic" (see Arab). Old English used Arabisc "Arabish." Originally in reference to gum arabic; noun meaning "Arabic language" is from late 14c.

Arabic numerals (actually Indian) first attested 1727; they were introduced in Europe by Gerbert of Aurillac (later Pope Sylvester II) after a visit to Islamic Spain in 967-970. A prominent man of science, he taught in the diocesan school at Reims, but the numbers made little headway against conservative opposition in the Church until after the Crusades. The earliest depiction of them in English, in "The Crafte of Nombrynge" (c. 1350) correctly identifies them as "teen figurys of Inde."
arable (adj.) Look up arable at Dictionary.com
early 15c., "suitable for plowing" (as opposed to pasture- or wood-land), from Old French arable (12c.), from Latin arabilis, from arare "to plow," from PIE *are- "to plow" (source also of Greek aroun, Old Church Slavonic orja, Lithuanian ariu "to plow;" Gothic arjan, Old English erian, Middle Irish airim, Welsh arddu "to plow;" Old Norse arþr "a plow"). By late 18c. it replaced native erable, from Old English erian "to plow," from the same PIE source.
arachnid (n.) Look up arachnid at Dictionary.com
"a spider," 1869, from French arachnide (1806) or Modern Latin Arachnida, introduced as name for this class of arthropods 1815 by French biologist Jean Baptiste Pierre Antoine de Monet de Lamarck (1744-1829), from Greek arakhne (fem.) "spider; spider's web," which probably is cognate with Latin aranea "spider, spider's web" (borrowed in Old English as renge "spider"), from aracsna. The Latin word could be a Greek borrowing or both could be from a common root. An earlier noun form was arachnidian (1828). The Latin word appears in English as arain, noted in John Ray's "Collection of English Words" (1768) as a Nottinghamshire word for "the larger kind of spiders."
arachnoid (adj.) Look up arachnoid at Dictionary.com
"cobweb-like," especially of the membrane around the brain and spinal cord, 1789, from Modern Latin arachnoides, from Greek arakhnoeides "cobweb-like," from arakhne "cobweb" (see arachnid) + -oeides (see -oid).
arachnologist (n.) Look up arachnologist at Dictionary.com
student of spiders, 1806; see arachnid + -ology. Related: Arachnology.
arachnophobia (n.) Look up arachnophobia at Dictionary.com
1925, from comb. form of arachnid + -phobia "fear."
Aragon Look up Aragon at Dictionary.com
medieval Spanish kingdom, named for a river that runs through it, probably from a PIE root meaning "water."
Aramaic Look up Aramaic at Dictionary.com
northern branch of Semitic language group, 1834, from biblical land of Aram, roughly corresponding to modern Syria; probably related to Hebrew and Aramaic rum "to be high," thus originally "highland." Aramaic became the lingua franca of the Assyrian empire and later for centuries was the official language of the Persian kingdom and the daily language of Israel at the time of Christ.
arational (adj.) Look up arational at Dictionary.com
"not purporting to be governed by laws of reason," 1935; see a- (2) + rational.
arbalest (n.) Look up arbalest at Dictionary.com
"crossbow," c. 1300, from Old French arbaleste "large crossbow with a crank" (12c., Modern French arbalète), from Vulgar Latin arbalista, from Late Latin arcuballista "catapult," from Latin arcus "bow" (see arc (n.)) + ballista "machine for throwing projectiles" (see ballistic). German armbrust is from the same French word but mangled by folk etymology.
arbiter (n.) Look up arbiter at Dictionary.com
late 14c., from Old French arbitre or directly from Latin arbiter "one who goes somewhere (as witness or judge)," in classical Latin used of spectators and eye-witnesses, in law, "he who hears and decides a case, a judge, umpire, mediator;" from ad- "to" (see ad-) + baetere "to come, go." The specific sense of "one chosen by two disputing parties to decide the matter" is from 1540s. The earliest form of the word attested in English is the fem. noun arbitress (mid-14c.) "a woman who settles disputes."
arbitrage (n.) Look up arbitrage at Dictionary.com
"exercise of the function of an arbitrator," late 15c., from Old French arbitrage "arbitration, judgment," from arbitrer "to arbitrate, judge," from Late Latin arbitrari, from Latin arbiter (see arbiter).
arbitrary (adj.) Look up arbitrary at Dictionary.com
early 15c., "deciding by one's own discretion," from Old French arbitraire (14c.) or directly from Latin arbitrarius "depending on the will, uncertain," from arbiter (see arbiter). The original meaning gradually descended to "capricious" and "despotic" (1640s). Related: Arbitrarily; arbitrariness.
arbitrate (v.) Look up arbitrate at Dictionary.com
1580s (arbitrable is recorded from 1530s), "to give an authoritative decision," from Latin arbitratus, past participle of arbitrari "be of an opinion, give a decision," from arbiter (see arbiter). Meaning "to act as an arbitrator" is from 1610s. Related: Arbitrated; arbitrating. The earlier verb form was arbitren (early 15c.).
arbitration (n.) Look up arbitration at Dictionary.com
late 14c., "absolute decision," from Old French arbitracion, from Latin arbitrationem (nominative arbitratio) "judgment, will," noun of action from past participle stem of arbitrari "to be of an opinion, give a decision," from arbiter (see arbiter). Meaning "settlement of a dispute by a third party" is from 1630s.
arbitrator (n.) Look up arbitrator at Dictionary.com
early 15c., from Old French arbitratour (13c.), from Latin arbitrator "a spectator, hearer, witness, judge," agent noun from past participle stem of arbitrari, from arbiter (see arbiter). The legal form of popular arbiter; in modern usage, an arbiter makes decisions of his own accord and is accountable to no one but himself; an arbitrator (early 15c.) decides issues referred to him by the parties.
arbitrer (n.) Look up arbitrer at Dictionary.com
late 14c., from Anglo-French arbitrour, Old French arbitreor (13c.), from Old French arbitrer (see arbitrage).
arbor (n.) Look up arbor at Dictionary.com
c. 1300, herber, "herb garden," from Old French erbier "field, meadow; kitchen garden," from Latin herba "grass, herb" (see herb). Later "a grassy plot" (early 14c., a sense also in Old French), "a shaded nook" (mid-14c.). Probably not from Latin arbor "tree," though perhaps influenced by its spelling.

The change from er- to ar- before consonants in Middle English also reflects a pronunciation shift: compare farm from ferme, harbor from Old English herebeorg.
Arbor Day Look up Arbor Day at Dictionary.com
the day set aside for the planting of trees, first celebrated 1872 in Nebraska, the brainchild of U.S. agriculturalist and journalist J. Sterling Morton (1832-1902). From Latin arbor "tree," which is of unknown origin.
arbor vitae (n.) Look up arbor vitae at Dictionary.com
type of evergreen shrub, 1660s, name given by French physician and botanist Charles de Lécluse (1525-1609), Latin, literally "tree of life." Also used in late 18c. rogue's slang as a cant word for "penis."
arboreal (adj.) Look up arboreal at Dictionary.com
1660s, from Latin arboreus "pertaining to trees," from arbor "tree," which is of unknown origin, + -al (1).
arboretum (n.) Look up arboretum at Dictionary.com
"tree-garden," 1838, from Latin arboretum, literally "a place grown with trees," from arbor "tree," which is of unknown origin, + -etum, suffix used to form the names of gardens and woods.
arborist (n.) Look up arborist at Dictionary.com
1570s, from Latin arbor "tree," which is of unknown origin, + -ist. In early use probably from French arboriste.
arbour (n.) Look up arbour at Dictionary.com
chiefly British English spelling of arbor (q.v.); for spelling, see -or.
arc (n.) Look up arc at Dictionary.com
late 14c., originally in reference to the sun's apparent motion in the sky, from Old French arc "bow, arch, vault" (12c.), from Latin arcus "a bow, arch," from PIE root *arku- "bowed, curved" (source also of Gothic arhvazna "arrow," Old English earh, Old Norse ör; also, via notion of "supple, flexible," Greek arkeuthos, Latvian ercis "juniper," Russian rakita, Czech rokyta, Serbo-Croatian rakita "brittle willow"). Electrical sense is from 1821.
arc (v.) Look up arc at Dictionary.com
1893, in the electrical sense, from arc (n.). Meaning "to move in an arc" attested by 1954. Related: Arced; arcing.
arcade (n.) Look up arcade at Dictionary.com
1731 (as arcado, from 1640s), from Italian arcata "arch of a bridge," from arco "arc," from Latin arcus (see arc). Applied to passages formed by a succession of arches, avenues of trees, and ultimately to any covered avenue, especially one lined with shops (1731) or amusements; hence arcade game (1977).
Arcadia Look up Arcadia at Dictionary.com
see Arcadian.
Arcadian Look up Arcadian at Dictionary.com
"ideally rustic or rural; an idealized rustic," 1580s, from Greek Arkadia, district in the Peloponnesus, taken by poets as an ideal region of rural felicity, traditionally from Arkas (genitive Arkadas), son of Zeus, name of the founder and first ruler of Arcadia.
arcana (n.) Look up arcana at Dictionary.com
"hidden things, mysteries," 1590s, a direct adoption of the Latin plural of arcanum "a secret, a mystery," from neuter of adjective arcanus "secret, hidden, private, concealed" (see arcane). Occasionally mistaken for a singular and pluralized as arcanas because arcana is far more common than arcanum.
arcane (adj.) Look up arcane at Dictionary.com
1540s, from Latin arcanus "secret, hidden, private, concealed," from arcere "close up, enclose, contain," from arca "chest, box, place for safe-keeping," from PIE *ark- "to hold, contain, guard" (source also of Greek arkos "defense," arkein "to ward off;" Armenian argel "obstacle;" Lithuanian raktas "key," rakinti "to shut, lock").