adversary (n.)
mid-14c., aduersere, from Anglo-French adverser (13c.), Old French adversaire "adversary, opponent, enemy," or directly from Latin adversarius "opponent, adversary, rival," noun use of adjective meaning "opposite, hostile, contrary," literally "turned toward one," from adversus "turned against" (see adverse). The Latin word is glossed in Old English by wiðerbroca.
adverse (adj.)
late 14c., "contrary, opposing," from Old French avers (13c., Modern French adverse) "antagonistic, unfriendly, contrary, foreign" (as in gent avers "infidel race"), from Latin adversus "turned against, turned toward, fronting, facing," figuratively "hostile, adverse, unfavorable," past participle of advertere, from ad- "to" (see ad-) + vertere "to turn" (see versus). Related: Adversely.
adversity (n.)
c.1200, aduersite "misfortune, hardship, difficulty," from Old French aversité "adversity, calamity, misfortune; hostility, wickedness, malice" (Modern French adversité), from Latin adversitatem (nominative adversitas) "opposition," from adversus (see adverse).
advert (n.)
colloquial shortening of advertisement, attested by 1860.
advert (v.)
mid-15c., averten "to turn (something) aside," from Middle French avertir (12c.), from Late Latin advertere (see advertise). The -d- added 16c. on the Latin model. Related: Adverted; adverting.
advertise (v.)
early 15c., "to take notice of," from Middle French advertiss-, present participle stem of a(d)vertir "to warn" (12c.), from Latin advertere "turn toward," from ad- "toward" (see ad-) + vertere "to turn" (see versus).

Sense shifted to "to give notice to others, warn" (late 15c.) by influence of advertisement; specific meaning "to call attention to goods for sale, rewards, etc." had emerged by late 18c. Original meaning remains in the verb advert "to give attention to." Related: Advertised; advertising.
advertised (adj.)
late 15c., "informed;" 1780s, "publicly announced," past participle adjective from advertise.
advertisement (n.)
early 15c., "written statement calling attention to" something, "public notice" (of anything, but often of a sale); from Middle French avertissement, from stem of avertir (see advertise). Meaning "public notice" (usually paid), the main modern sense, emerged 1580s and was fully developed by 18c.
advertiser (n.)
1560s, agent noun from advertise (v.).
advice (n.)
late 13c., auys "opinion," from Old French avis "opinion, view, judgment, idea" (13c.), from phrase ço m'est à vis "it seems to me," or from Vulgar Latin *mi est visum "in my view," ultimately from Latin visum, neuter past participle of videre "to see" (see vision).

The unhistorical -d- was introduced in English 15c., on model of Latin words in ad-. Substitution of -c- for -s- is 18c., to preserve the breath sound and to distinguish from advise. Meaning "opinion given as to action, counsel" is from late 14c.
advisability (n.)
1778 (in a letter from George Washington at Valley Forge), from advisable + -ity.
advisable (adj.)
1640s, from advise (v.) + -able.
advise (v.)
late 13c., avisen "to view, consider," from Old French aviser "deliberate, reflect, consider" (13c.), from avis "opinion" (see advice). Meaning "to give counsel to" is late 14c. Related: Advised; advising.
advisement (n.)
early 14c., avisement "examination, inspection, observation," from Old French avisement "consideration, reflection," from aviser (see advise). Meaning "advice, counsel" is from c.1400, as is that of "consultation, conference."
adviser (n.)
1610s, agent noun from advise (v.). Meaning "military person sent to help a government or army in a foreign country" is recorded from 1915. Alternative form, Latinate advisor, is perhaps a back-formation from advisory.
advisory (adj.)
1778; see advise + -ory. The noun meaning "weather warning" is from 1931.
advocacy (n.)
late 14c., from Old French avocacie (14c.), from Medieval Latin advocatia, noun of state from Latin advocatus (see advocate (n.)).
advocate (n.)
mid-14c., "one whose profession is to plead cases in a court of justice," a technical term from Roman law, from Old French avocat "barrister, advocate, spokesman," from Latin advocatus "one called to aid; a pleader, advocate," noun use of past participle of advocare "to call" (as witness or advisor) from ad- "to" (see ad-) + vocare "to call," related to vocem (see voice (n.)). Also in Middle English as "one who intercedes for another," and "protector, champion, patron." Feminine forms advocatess, advocatrice were in use in 15c.
advocate (v.)
1640s, from advocate (n.). Related: Advocated; advocating; advocation.
adware (n.)
2000 (earlier as the name of a software company), from ad (n.) + -ware, abstracted from software, etc.
adze (n.)
also adz, Middle English adese, adse, from Old English adesa "adze, hatchet," of unknown origin, perhaps somehow related to Old French aisse, Latin ascia "axe" (see ax). Spelling with -z- is from 18c. Adze "has been monosyllabic only since the seventeenth century. The word has no cognates, though it resembles the names of the adz and the hammer in many languages" [Liberman, 2008].
ae
see æ. As a word, it can represent Old English æ "law," especially law of nature or God's law; hence "legal custom, marriage."
Aegean
sea between Greece and Asia Minor, 1570s, traditionally named for Aegeus, father of Theseus, who threw himself to his death in it when he thought his son had perished; but perhaps from Greek aiges "waves," a word of unknown origin.
aegis (n.)
"protection," 1793, from Latin aegis, from Greek Aigis, the name of the shield of Zeus, said by Herodotus to be related to aix (genitive aigos) "goat," from PIE *aig- "goat" (cognates: Sanskrit ajah, Lithuanian ozys "he-goat"), as the shield was of goatskin. Athene's aigis was a short goat-skin cloak, covered with scales, set with a gorgon's head, and fringed with snakes. The exact use and purpose of it is not now clear.
The goatskin would be worn with the two forelegs tied in front of the wearer's breast, or possibly with the head passed through an opening made at the neck, by the removal of the animal's head. [F. Warre Cornish, ed., "Dictionary of Greek and Roman Antiquities," London, 1898]
aegrotat (n.)
certificate that a student is ill, Latin, literally "he is sick," third person singular of aegrotare "to be sick," from aeger "sick."
Aeneas
hero of the "Æneid," son of Anchises and Aphrodite, Latin, from Greek Aineias, of unknown origin, perhaps literally "praise-worthy," from ainos "tale, story, saying, praise" (related to enigma); or perhaps related to ainos "horrible, terrible." The Aeneid (late 15c. in English) is literally "of or pertaining to Aeneas," from French Enéide, Latin Æneida.
Aeolian (adj.)
c.1600, "of the wind," from Latin Æolus "god of the winds," from Greek Aiolos, from aiolos "quickly moving." Æolian harp first recorded 1791. The ancient district of Aiolis in Asia Minor was said to have been named for the wind god, hence Æolian also refers to one branch of the ancient Greek people.
Aeolus
see Aeolian.
aeon (n.)
1640s; see eon.
aerate (v.)
1794, from Latin aer (genitive aeris; see air (n.1)) + verbal suffix -ate (2). Related: Aerated; aerating.
aeration (n.)
1570s, from French aération, from aérer (v.), from Latin aer (see air (n.1)). In some cases, from aerate.
aerial (adj.)
c.1600, from Latin aerius "airy, aerial, lofty, high" (from Greek aerios "of the air, pertaining to air," from aer "air;" see air (n.1)) + adjectival suffix -al (1).
aerial (n.)
1902 (short for aerial antenna, etc.); see aerial (adj.).
aerie (n.)
"eagle's nest," 1580s (attested in Anglo-Latin from early 13c.), from Old French aire "nest," Medieval Latin area "nest of a bird of prey" (12c.), perhaps from Latin area "level ground, garden bed" [Littré], though some doubt this [Klein]. Another theory connects it to atrium. Formerly misspelled eyrie (1660s) on the mistaken assumption that it derived from Middle English ey "egg."
aero-
word-forming element meaning "air, atmosphere; aircraft; gases," from Greek aero-, comb. form of aer (genitive aeros) "air, lower atmosphere" (see air (n.1)).
aerobatics (n.)
aircraft tricks, "trick flying," 1914, from aero- + ending from acrobat (also see -ics). Earlier (1879) it meant "the art of constructing and using airships; aerial navigation; aeronautics."
aerobic (adj.)
"living only in the presence of oxygen," 1875, (after French aérobie, coined 1863 by Louis Pasteur) from Greek aero- "air" (see aero-) + bios "life" (see bio-).
aerobics (n.)
method of exercise and a fad in early 1980s, American English, coined 1968 by Kenneth H. Cooper, U.S. physician, from aerobic (also see -ics) on the notion of activities which require modest oxygen intake and thus can be maintained.
aerodonetics (n.)
science of gliding, 1907, from Greek aero- "air" (see aero-) + stem of donein "to shake, drive about." Also see -ics.
aerodrome (n.)
1902, from aero- on analogy of hippodrome. Earlier (1891) a name for a flying machine.
aerodynamic (adj.)
also aero-dynamic, 1847; see aero- + dynamic (adj.). Compare German aerodynamische (1835), French aérodynamique.
aerodynamics (n.)
1837, from aero- "air" + dynamics.
aerofoil (n.)
1907, from aero- + foil (n.).
aeronautics (n.)
1824, from aeronautic (1784), from French aéronautique, from aéro- (see aero-) + nautique "of ships," from Latin nauticus, from Greek nautikos (see nautical). Originally of balloons. Also see -ics. Aeronaut "balloonist" is from 1784.
aerophyte (n.)
1840, perhaps via French aerophyte, from aero- + -phyte "plant."
aeroplane (n.)
1866, from French aéroplane (1855), from Greek aero- "air" (see air (n.1)) + stem of French planer "to soar," from Latin planus "level, flat" (see plane (n.1)). Originally in reference to surfaces (such as the protective shell casings of beetles' wings); meaning "heavier than air flying machine" first attested 1873, probably an independent English coinage (see airplane).
aerosol (n.)
1919, from aero- "air" + first syllable in solution. A term in physics; modern commercial application is from 1940s.
aerospace (adj.)
1958, American English, from aero- "atmosphere" + (outer) space (n.).
Aeschylus
Greek Aiskhylos, Athenian soldier, poet, and playwright, Father of Tragedy (525-456 B.C.E.).
Aesir (n.)
chief gods of Scandinavian religion, from Old Norse plural of ass "god," related to Old English os, Gothic ans "god" (see Asgard).