Online Etymology Dictionary

archaebacteria (n.): plural of archaebacterium (1977), from archaeo- + bacterium (see bacteria).
archaeo-: before vowels archae-, word-forming element meaning "ancient, olden, primitive, primeval, from the beginning," from Latinized form of Greek arkhaio-, comb. form of arkhaios "ancient," from arkhe "beginning" (see archon).
archaeoastronomy (n.): 1971, from archaeo- + astronomy.
archaeologist (n.): 1824; see archaeology + -ist.
archaeology (n.): c. 1600, "ancient history," from French archéologie (16c.) or directly from Greek arkhaiologia "the study of ancient things;" see archaeo- + -ology. Meaning "scientific study of ancient peoples" recorded by 1825. Related: Archaeological; archaeologically.
archaeopteryx (n.): oldest known fossil bird, 1859, Modern Latin, from archaeo- "ancient, primitive" + Greek pteryx "wing" (see pterodactyl).
archaic (adj.): 1810, from or by influence of French archaique (1776), ultimately from Greek arkhaikos "old-fashioned," from arkhaios "ancient," from arkhe "beginning" (see archon). Archaical is attested from 1799.
archaism (n.): 1640s, "retention of what is old and obsolete," from Modern Latin archaismus, from Greek arkhaismos, from arkhaizein "to copy the ancients" (in language, etc.); see archaic. Meaning "an archaic word or expression" is from c. 1748.
archangel (n.): late 12c., from Old French archangel (12c.) or directly from Late Latin archangelus, from Greek arkhangelos "chief angel," from arkh- "chief, first" (see archon) + angelos (see angel). Replaced Old English heah encgel.
archangelic (adj.): mid-15c.; see archangel + -ic.
archbishop (n.): Old English ærcebiscop, from Late Latin archiepiscopus, from Greek arkhi- "chief" (see archon) + episkopos "bishop," literally "overseer." Replaced earlier Old English heah biscop (see bishop). The spelling conformed to Latin from 12c.
archbishopric (n.): Old English arcebiscoprice, from archbishop + rice "realm, dominion, province" (see regal).
archdeacon (n.): Old English arcediacon, from Church Latin archidiaconus, from Ecclesiastical Greek arkhidiakonon "chief deacon;" see arch- + deacon.
archdiocese (n.): 1762, from arch- + diocese.
archduchess (n.): 1610s; see arch- + duchess. Also compare archduke.
archduke (n.): 1520s, from Middle French and Old French archeduc, from Merovingian Latin archiducem (c.750); see arch- + duke (n.). Formerly the title of the rulers of Austrasia, Lorraine, Brabant, and Austria; later the titular dignity of the sons of the Emperor of Austria. Related: Archducal; archduchy.
archenemy (n.): also arch-enemy, 1540s, from arch- + enemy.
archeological (adj.): alternative spelling of archaeological (see archaeology). Also see ae.
archeologist (n.): alternative spelling of archaeologist. Also see ae.
archeology (n.): alternative spelling of archaeology. Also see ae.
archer (n.): late 13c., from Anglo-French archer, Old French archier "archer, bowmaker," from Latin arcarius, from arcus "bow" (see arc). Also a 17c. name for the bishop in chess.
archery (n.): c. 1400, from Anglo-French archerye, Old French archerie, from archier "archer" (see archer).
archetypal (adj.): 1640s, from Latin archetypum (see archetype) + -al (1). Jungian sense is from 1923.
archetype (n.): "original pattern from which copies are made," 1540s [Barnhart] or c. 1600 [OED], from Latin archetypum, from Greek arkhetypon "pattern, model, figure on a seal," neuter of adjective arkhetypos "first-moulded," from arkhe- "first" (see archon) + typos "model, type, blow, mark of a blow" (see type). Jungian psychology sense of "pervasive idea or image from the collective unconscious" is from 1919. Jung defined archetypal images as "forms or images of a collective nature which occur practically all over the earth as constituents of myths and at the same time as autochthonous individual products of unconscious origin." ["Psychology and Religion" 1937]
archfiend (n.): 1667, from arch (adj.) + fiend (n.). Originally and typically Satan (arch-foe "Satan" is from 1610s).
So stretcht out huge in length the Arch-fiend lay. ["Paradise Lost," 1667]
Archibald: masc. proper name, from Old High German Erchanbald, literally "genuine bold," from erchan "genuine" + bald (see bold). Archie, British World War I military slang for "German anti-aircraft fire" (1915) supposedly is from black humor of airmen dodging hostile fire and thinking of the refrain of a popular music hall song, "Archibald, certainly not!"
archipelago (n.): c. 1500, from Italian arcipelago "the Aegean Sea" (13c.), from Greek arkhipelagos, from arkhi- "chief" (see archon) + pelagos "sea" (see pelagic). The Aegean Sea being full of island chains, the meaning was extended in Italian to "any sea studded with islands." Klein, noting the absence of arkhipelagos in ancient or Medieval Greek (the modern word in Greek is borrowed from Italian) believe it is an Italian mistake for Aigaion pelagos "Aegean Sea" (Medieval Latin Egeopelagus), or influenced by that name.
architect (n.): 1550s, from Middle French architecte, from Latin architectus, from Greek arkhitekton "master builder, director of works," from arkhi- "chief" (see archon) + tekton "builder, carpenter" (see texture). An Old English word for it was heahcræftiga "high-crafter."
architectonic (adj.): 1670s (architectonical is from c. 1600), "pertaining to architecture," from Latin architectonicus, from Greek arkhitektonikos "pertaining to a master builder," from arkhitekton (see architect). Metaphysical sense, "pertaining to systematization of knowledge," is from 1801.
architectural (adj.): 1762; see architecture + -al (1). Related: Architecturally.
architecture (n.): 1560s, from Middle French architecture, from Latin architectura, from architectus "architect" (see architect).
architrave (n.): 1560s, from Italian architrave, from archi- "beginning, origin" (see archon) + trave "beam," from Latin trabem (nominative trabs) "beam, timber," from PIE *treb- "dwelling" (see tavern).
archival (adj.): 1800; see archives + -al (1). Related: Archivally.
archive (v.): 1819 (implied in archived), from archives. Related: Archiving.
archives (n.): c. 1600, from French archif (16c.), from Late Latin archivum (singular), from Greek ta arkheia "public records," plural of arkheion "town hall," from arkhe "government," literally "beginning, origin, first place" (see archon).
archivist (n.): 1753, from Medieval Latin or Italian archivista or French archiviste (see archives).
archon (n.): one of the nine chief magistrates of ancient Athens, 1650s, from Greek arkhon "ruler," noun use of present participle of arkhein "to rule," from PIE *arkhein- "to begin, rule, command," a "Gk. verb of unknown origin, but showing archaic Indo-European features ... with derivatives arkhe, 'rule, beginning,' and arkhos, 'ruler' " [Watkins].
archrival (n.): by 1805, from arch- + rival (n.).
archway (n.): 1802, from arch (n.) + way (n.).
Arctic (adj.): late 14c., artik, from Old French artique, from Medieval Latin articus, from Latin arcticus, from Greek arktikos "of the north," literally "of the (constellation) Bear," from arktos "bear; Ursa Major; the region of the north," the Bear being a northerly constellation. From *rkto-, the usual Indo-European base for "bear" (source also of Avestan aresho, Armenian arj, Albanian ari, Latin ursus, Welsh arth); see bear (n.) for why the name changed in Germanic. The -c- was restored from 1550s. As a noun, "the Arctic regions," from 1560s.
Arctic Circle: 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: 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.): "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.): 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.): 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.): 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.): chiefly British English spelling of ardor (q.v.); for spelling, see -or.
arduous (adj.): 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.): "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.): 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!").