Online Etymology Dictionary

approximately (adv.): 1742, from approximate (adj.) + -ly (2).
approximation (n.): early 15c., "act of coming near or close," noun of action from approximate (v.). Meaning "result of approximating" is from 1650s.
appurtenance (n.): c.1300, "right, privilege or possession subsidiary to a principal one," from Anglo-French apurtenance (12c.), Old French apartenance, present participle of apartenir "be related to," from Latin appertinere "to pertain to," from ad- "to" (see ad-) + pertinere "belong to" (see pertain).
appurtenances (n.): "apparatus, gear," late 14c.; see appurtenance.
appurtenant (adj.): late 14c., from Anglo-French apurtenant, Old French apartenant, present participle of apartenir "be related to" (see appurtenance).
apraxia (n.): 1877, medical Latin, from German apraxie (H. Steinthal, 1871), from Greek apraxia "inaction," from privative prefix a- (see a- (3)) + praxis "a doing, action, business" (see praxis).
apricate (v.): 1690s, "to bask in the sun," from Latin apricatus, past participle of apricari "to bask in the sun," from apricus "exposed" (to the sun); perhaps contracted from *apericus, from aperire "to open." Transitive sense is recorded from 1851.
apricot (n.): 1550s, abrecock, from Catalan abercoc, related to Portuguese albricoque, from Arabic al-birquq, through Byzantine Greek berikokkia from Latin (malum) praecoquum "early-ripening (fruit)" (see precocious). Form assimilated to French abricot.
Latin praecoquis early-ripe, can probably be attributed to the fact that the fruit was considered a variety of peach that ripened sooner than other peaches .... [Barnhart]
The older Latin name for it was prunum Armeniacum or malum Armeniacum, in reference to supposed origin in Armenia. As a color name, first attested 1906.
April: c.1300, aueril, from Old French avril (11c.), from Latin (mensis) Aprilis "(month) of Venus," second month of the ancient Roman calendar, dedicated to the goddess Venus and perhaps based on Apru, an Etruscan borrowing of Greek Aphrodite. In English in Latin form from mid-12c. Replaced Old English Eastermonað, which was similarly named for a fertility goddess. Re-spelled in Middle English on Latin model (apprile first attested late 14c.).
April fool (n.): 1680s; April-gowk (from Old Norse gaukr "a cuckoo") is a northern variant. April Fool's Day customs of sending people on false errands seem to have come to England from France late 17c.; originally All Fool's Day (1712). In Cumberland, Westmorland and northern parts of Lancashire and Yorkshire, however, May 1 was the day for hoaxing, and the fool was a May gosling. That custom was first attested 1791.
apron (n.): mid-15c., faulty separation (cf. adder, umpire) of a napron (c.1300), from Old French naperon "small table-cloth," diminutive of nappe "cloth," from Latin mappa "napkin." Napron was still in use as recently as late 16c. The shift of Latin -m- to -n- was a tendency in Old French (e.g. conter from computare, printemps from primum, natte "mat, matting," from matta). Symbolic of "wife's business" from 1610s. Apron-string tenure was in reference to property held in virtue of one's wife, or during her lifetime only.
Even at his age, he ought not to be always tied to his mother's apron string. [Anne Brontë, "The Tenant of Wildfell Hall," 1848]
apropos (adv.): 1660s, "opportunely," from French à propos "to the purpose," from propos "thing said in conversation, talk; purpose, plan," from Latin propositium "purpose," past participle of proponere "to set forth, propose" (see propound). Meaning "as regards" is 1761, from French. As an adjective, "to the point or purpose," from 1690s.
apse (n.): "semicircular extension at the end of a church," 1846, from Latin apsis "an arch, a vault," from Greek hapsis (Ionic apsis) "loop, arch," originally "a fastening, felloe of a wheel," from haptein "fasten together," of unknown origin. The original sense in Greek seems to have been the joining of the arcs to form a circle, especially in making a wheel. The architectural term is earlier attested in English in the Latin form (1706).
apsis (n.): "perigree of the moon, perihelion of a planet" (plural apsides), 1650s, from Latin apsis "arch, vault" (see apse).
apt (adj.): mid-14c., "inclined, disposed;" late 14c., "suited, fitted, adapted," from Old French ate (13c., Modern French apte), or directly from Latin aptus "fit, suited," adjectival use of past participle of *apere "to attach, join, tie to," from PIE root *ap- "to grasp, take, reach" (cf. Sanskrit apnoti "he reaches," Latin apisci "to reach after, attain," Hittite epmi "I seize"). Elliptical sense of "becoming, appropriate" is from 1560s.
aptitude (n.): early 15c., "tendency, likelihood," from Middle French aptitude (14c.) or directly from Late Latin aptitudo (genitive aptitudinis) "fitness," noun of quality from Latin aptus "joined, fitted" (see apt). Meaning "natural capacity to learn" is 1540s; that of "quality of being fit (for a purpose or position)" is from 1640s.
aptly (adv.): early 15c., "by natural means," from apt + -ly (2).
aptness (n.): 1530s, from apt + -ness.
aqua (n.): "water," late 14c.; see aqua-. Used in late Middle English in combinations to mean "decoction, solution" (cf. aqua regia, a mix of concentrated acids, literally "royal water," so called for its power to dissolve gold and other "noble" metals). As the name of a light greenish-blue color, 1936.
aqua fortis (n.): old name for "concentrated nitric acid," c.1600, Latin, literally "strong water;" see aqua- + fort. So called for its power of dissolving metals (copper, silver) unaffected by other agents.
aqua vitae (n.): early 15c., Latin, literally "water of life," an alchemical term for unrefined alcohol. Applied to brandy, whiskey, etc. from 1540s. Cf. whiskey, also French eau-de-vie "spirits, brandy," literally "water of life."
aqua-: word-forming element meaning "water," from Latin aqua "water; the sea; rain," cognate with Proto-Germanic *akhwo, source of Old English ea "river," Gothic ahua "river, waters," Old Norse Ægir, name of the sea-god, Old English ieg "island;" all from PIE *akwa- "water" (cf. Sanskrit ap "water," Hittite akwanzi "they drink," Lithuanian uppe "a river").
aquacade (n.): "aquatic entertainment," 1937, American English, from aqua- + -cade, from cavalcade (q.v.).
aquaculture (n.): 1869, from aqua- + culture (n.).
aqualung (n.): 1950, from aqua- + lung. Developed 1943 by Jacques Cousteau and Emile Gagnan.
aquamarine (n.): 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.): 1881, from aqua- + ending from Greek nautes "sailor" (see naval).
aquarelle (n.): 1855, from French aquarelle (18c.), from Italian acquerella "water-color," diminutive of acqua, from Latin aqua "water" (see aqua-).
Aquarian (adj.): 1940, in the astrological/New Age sense; see Aquarius + -ian.
aquarium (n.): 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: 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.): 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.): 1782, "engraving made with aqua fortis," from Italian acquatinta, from Latin aqua tincta "dyed water;" see aqua- + tinct.
aqueduct (n.): 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.): 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.): 1897, coined from Latin aqui-, comb. form of aqua "water" (see aqua-) + -fer "bearing," from ferre "to bear" (see infer).
aquiline (adj.): "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," of uncertain origin, usually explained as "the dark bird;" cf. aquilus "blackish, of the color of darkness."
aquiver (adv.): 1864, from a- (1) + quiver (v.).
Arab (n.): 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.): 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: 1711; see Arab + -ia. The older name for "the country of Arabia" was Araby (late 13c.).
Arabian: 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.): 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.): 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" (cf. 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"). Replaced by late 18c. native erable, from Old English erian "to plow," from the same PIE source.
arachnid (n.): "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," 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).
arachnoid (adj.): "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.): student of spiders, 1806; see arachnid + -ology. Related: Arachnology.
arachnophobia (n.): 1925, from comb. form of arachnid + -phobia "fear."
Aragon: medieval Spanish kingdom, named for a river that runs through it, probably from a PIE root meaning "water."
Aramaic: 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."