Online Etymology Dictionary

abyss (n.): late 14c., earlier abime (c. 1300, from a form in Old French), from Late Latin abyssus "bottomless pit," from Greek abyssos (limne) "bottomless (pool)," from a- "without" (see a- (2)) + byssos "bottom," possibly related to bathos "depth."
abyssal (adj.): 1690s, used especially of the zone of ocean water below 300 fathoms, from abyss + -al (1). Though the 19th century, abysmal was more common in oceanography.
Abyssinia (n.): old name for Ethiopia, 1630s, from Modern Latin Abyssinia, from Arabic Habasah, the name for the region, said to be from Amharic hbsh "mixed," in reference to the different races dwelling there. In 1920s-30s popular as a slang pun for "I'll be seeing you." Related: Abyssinian.
AC: abbreviation of air conditioning, by 1966.
AC/DC (adj.): electronics abbreviation of alternating current/direct current, by 1898. As slang for "bisexual," 1959, said to have been in use orally from c. 1940; the notion is of working both ways.
acacia (n.): 1540s, from Latin acacia, from Greek akakia "thorny Egyptian tree," perhaps related to Greek ake "point, thorn," from PIE root *ak- "sharp" (see acrid). Or perhaps a Hellenization of some Egyptian word. From late 14c. in English as the name of a type of gum used as an astringent, etc.
Academe (n.): "The Academy," 1580s, from phrase groves of Academe, translating Horace's silvas Academi (see academy); general sense of "the world of universities and scholarship" is attested from 1849. With lower-case letter, academia in the sense of "academic community" is from 1956.
Academe properly means Academus (a Greek hero); & its use as a poetic variant for academy, though sanctioned by Shakespeare, Tennyson & Lowell, is a mistake; the grove of A., however, (Milton) means rightly The Academy. [Fowler]
academic (adj.): 1580s, "relating to an academy," also "collegiate, scholarly," from Latin academicus "of the Academy," from academia (see academy). Meaning "theoretical, not practical, not leading to a decision" (such as university debates or classroom legal exercises) is from 1886. Academic freedom is attested from 1901. Related: Academically.
academy (n.): late 15c., "the classical Academy," from French Académie, from Latin Academia, from Greek Akademeia "grove of Akademos," a legendary Athenian of the Trojan War tales (his name apparently means "of a silent district"), whose estate, six stadia from Athens, was the enclosure where Plato taught his school.
The A[cademy], the Garden, the Lyceum, the Porch, the Tub, are names used for the five chief schools of Greek philosophy, their founders, adherents, & doctrines: the A., Plato, the Platonists & Platonism; the Garden, Epicurus, the Epicureans, & Epicureanism; the Lyceum, Aristotle, the Aristotelians, & Aristotelianism; the Porch, Zeno, the Stoics, & Stoicism; the Tub, Antisthenes, the Cynics, & Cynicism. [Fowler]
Sense broadened 16c. into "any school or training place." Academy awards (1941) so called for their distributor, the Academy of Motion Picture Arts and Sciences.
Acadian: 1705, from Acadia, Latinized form of Acadie, French name of Nova Scotia, probably from Archadia, the name given to the region by Verrazano in 1520s, from Greek Arkadia, emblematic in pastoral poetry of a place of rural peace (see Arcadian); the name may have been suggested to Europeans by the native Micmac (Algonquian) word akadie "fertile land." The Acadians, expelled by the English in 1755, settled in large numbers in Louisiana (see Cajun, which is a corruption of Acadian).
acanthus (n.): 1660s, from Latin acanthus, from Greek akanthos, from ake "point, thorn" (see acrid) + anthos "flower" (see anther). So called for its large spiny leaves. A conventionalized form of the leaf is used in Corinthian capitals.
Acapulco: in full, Acapulco de Juarez, resort town in western Mexico, from Nahuatl (Aztecan) acapulco "place of the large canes," from aca(tl) "cane (plant)" + -pul "large" + -co "place." Acapulco gold as the name of a local grade of potent marijuana is attested from 1965.
accede (v.): early 15c., from Latin accedere "approach, enter upon," from ad- "to" (see ad-) + cedere "go, move" (see cede). Latin ad- usually became ac- before "k" sounds. Related: Acceded; acceding.
accelerant (n.): 1854, from Latin accelerantem (nominative accelerans), present participle of accelerare "to hasten, quicken" (see accelerate). As an adjective from 1890.
accelerate (v.): 1520s, from Latin acceleratus, past participle of accelerare "to hasten, quicken," from ad- "to" (see ad-) + celerare "hasten," from celer "swift" (see celerity). Related: Accelerated; accelerating.
acceleration (n.): 1530s, from Latin accelerationem (nominative acceleratio) "a hastening," noun of action from past participle stem of accelerare "to hasten, quicken" (see accelerate).
accelerator (n.): 1610s, from Latin accelerator, agent noun from accelerare (see accelerate). Motor vehicle sense is from 1900.
accent (n.): late 14c., "particular mode of pronunciation," from Middle French accent, from Old French acent (13c.), from Latin accentus "song added to speech," from ad- "to" (see ad-) + cantus "a singing," past participle of canere "to sing" (see chant (v.)). Loan-translation of Greek prosoidia, from pros- "to" + oide "song," which apparently described the pitch scheme in Greek verse. The decorating sense of "something that emphasizes or highlights" is from 1972.
accent (v.): "to pronounce with accent or stress," 1520s, from Middle French accenter, from Old French acenter, from acent (see accent (n.)). Related: Accented; accenting.
accentuate (v.): 1731, from Medieval Latin accentuatus, past participle of accentuare "to accent," from Latin accentus (see accent (n.)). Originally "to pronounce with an accent;" meaning "emphasize" is recorded from 1865.
You've got to accentuate the positive
Eliminate the negative
Latch on to the affirmative
Don't mess with Mister In-Between

["Ac-Cent-Tchu-Ate the Positive," 1944, music by Harold Arlen, lyrics by Johnny Mercer]
Related: Accentuated; accentuating.
accentuation (n.): 1690s, from Medieval Latin accentuationem (nominative accentuatio) "intoning, chanting," noun of action from past participle stem of accentuare (see accentuate).
accept (v.): late 14c., "to take what is offered," from Old French accepter (14c.) or directly from Latin acceptare "take or receive willingly," frequentative of accipere "receive," from ad- "to" (see ad-) + capere "to take" (see capable). Related: Accepted; accepting.
acceptability (n.): 1660s, from Late Latin acceptabilitas, from Latin acceptabilis "worthy of acceptance" (see acceptable).
acceptable (adj.): late 14c., from Old French acceptable, from Latin acceptabilis "worthy of acceptance," from acceptare "take or receive willingly" (see accept). Related: Acceptably.
acceptance (n.): 1570s, from Middle French acceptance, from accepter (see accept). Earlier in same sense was acceptation (late 14c.).
access (n.): early 14c., "an attack of fever," from Old French acces "onslaught, attack; onset (of an illness)" (14c.), from Latin accessus "a coming to, an approach," noun use of past participle of accedere "to approach" (see accede). The later senses are directly from Latin. Meaning "an entrance" is from c. 1600. Meaning "habit or power of getting into the presence of (someone or something)" is from late 14c.
access (v.): 1962, originally in computing, from access (n.). Related: Accessed; accessing.
accessibility (n.): c. 1800, from accessible + -ity.
accessible (adj.): c. 1400, "affording access," from Middle French accessible, from Late Latin accessibilis, verbal adjective from Latin accessus "a coming near, approach" (see access (n.)). Meaning "easy to reach" is from 1640s; Of art or writing, "able to be readily understood," 1961 (a term not needed in the years before writing or art often deliberately was made not so).
accession (n.): "act of coming to a position," especially of a throne, 1640s, from Latin accessionem (nominative accessio) "a going to, joining, increase," noun of action from past participle stem of accedere "approach, enter upon" (see accede).
accessorize (v.): 1939, from accessory + -ize. Related: Accessorized; accessorizing.
accessory (n.): also accessary, early 15c. as a legal term in the criminal sense of "one aiding in a crime;" also "that which is subordinate to something else," from Late Latin accessorius, from accessor, agent noun from accedere "to approach" (see accede). Attested from 1896 as "woman's smaller articles of dress;" hence accessorize.
accessory (adj.): 1550s, "subordinate," from Late Latin accessorius, from accessor, agent noun from accedere "to approach" (see accede). Meaning "aiding in crime" is from c. 1600.
accidence (n.): late 14c., in philosophy, "non-essential or incidental characteristic," also "part of grammar dealing with inflection" (mid-15c.), in some cases a misspelling of accidents, or else directly from Latin accidentia (used as a term in grammar by Quintilian), neuter plural of accidens, present participle of accidere (see accident). The grammar sense is because they change in accordance with use.
accident (n.): late 14c., "an occurrence, incident, event," from Old French accident (12c.), from Latin accidentem (nominative accidens), present participle of accidere "happen, fall out, fall upon," from ad- "to" (see ad-) + cadere "fall" (see case (n.1)). Meaning grew from "something that happens, an event," to "something that happens by chance," then "mishap." Philosophical sense "non-essential characteristic of a thing" is late 14c. Meaning "unplanned child" is attested by 1932.
accidental (adj.): late 14c., "non-essential," from Old French accidentel or directly from Medieval Latin accidentalis, from Latin accidentem (see accident). Meaning "outside the normal course of nature" is from early 15c.; that of "coming by chance" is from 1570s.
accidental (n.): late 14c., "non-essential quality," from accidental (adj.). The musical sense is from 1868.
accidentally (adv.): late 14c., "non-essentially," also "unnaturally," from accidental + -ly (2). Meaning "unintentionally" is recorded from 1580s; phrase accidentally on purpose is recorded from 1862.
acclaim (v.): early 14c., "to lay claim to," from Latin acclamare "to cry out at" (see acclamation); the meaning "to applaud" is recorded by 1630s. Related: Acclaimed; acclaiming.
acclaim (n.): "act of acclaiming," 1667 (in Milton), from acclaim (v.).
acclamation (n.): 1540s, from Latin acclamationem (nominative acclamatio) "a calling, exclamation, shout of approval," noun of action from past participle stem of acclamare "shout approval or disapproval of, cry out at," from ad- "toward" (see ad-) + clamare "cry out" (see claim (v.)). As a method of voting en masse, by 1801, probably from the French Revolution.
acclimate (v.): 1792, from French acclimater, verb formed from à "to" (see ad-) + climat (see climate). Related: Acclimated; acclimating. The extended form acclimatize is now more common.
acclimation (n.): 1826, noun of action from acclimate.
acclimatize (v.): 1836; see acclimate + -ize; a more recent formation than acclimate and replacing it in many uses. Related: Acclimatized; acclimatizing.
acclivity (n.): 1610s, from Latin acclivitatem (nominative acclivitas) "an ascending direction, an upward steepness," from acclivis "mounting upwards, ascending," from ad- "up" (see ad-) + clivus "hill, a slope," from PIE *klei-wo-, suffixed form of *klei- "to lean" (see lean (v.)).
accolade (n.): 1620s, from French accolade (16c.), from Provençal acolada or Italian accollata, ultimately from noun use of a fem. past participle from Vulgar Latin *accollare "to embrace around the neck," from Latin ad- "to" (see ad-) + collum "neck" (see collar (n.)).

The original sense is of an embrace about the neck or the tapping of a sword on the shoulders to confer knighthood. Extended meaning "praise, award" is from 1852. Also see -ade. Earlier was accoll (mid-14c.), from Old French acolee "an embrace, kiss, especially that given to a new-made knight," from verb acoler. The French noun in the 16c. was transformed to accolade, with the foreign suffix.
accommodate (v.): 1530s, from Latin accomodatus "suitable," past participle of accomodare "make fit, adapt, fit one thing to another," from ad- "to" (see ad-) + commodare "make fit," from commodus "fit" (see commode). Related: Accommodated; accommodating.
accommodating (adj.): "obliging," 1771, present participle adjective from accommodate.
accommodation (n.): "room and provisions, lodging," c. 1600, now usually plural (accommodations) and chiefly U.S.; from French accommodation, from Latin accommodationem (nominative accommodatio), noun of action from past participle stem of accommodare (see accommodate). Meaning "appliance, anything which affords aid" is from 1610s; that of "act of accommodating" is from 1640s.
accommodations (n.): "lodgings and entertainment," see accommodation.