late 14c., "an occurrence, incident, event; what comes by chance," from Old French accident (12c.), from Latin accidentem (nominative accidens) "an occurrence; chance; misfortune," noun use of present participle of accidere "happen, fall out, fall upon," from ad "to" (see ad-) + combining form of cadere "to fall" (from PIE root *kad- "to fall").

The sense has had a tendency since Latin to extend from "something that happens, an event" to "a mishap, an undesirable event." Latin si quid cui accidat, "if anything should happen to one," was a euphemism for "if one should die." In Middle English the word is met usually in theology (in reference to the material qualities in the sacramental bread and wine), medicine ("something out of the ordinary, disease, injury"), or philosophy ("non-essential characteristic of a thing").

From late 15c. as "the operations of chance." Meaning "an unplanned child" is attested by 1932. Accident-prone is from 1926.

late 14c., "non-essentially," also "unnaturally," from accidental (adj.) + -ly (2). Meaning "unintentionally" is recorded from 1580s; phrase accidentally on purpose is recorded from 1799.

late 14c., "non-essential," from Old French accidentel or directly from Medieval Latin accidentalis, from Latin accidentem "an accident, chance" (see accident). Meaning "outside the normal course of nature" is from early 15c.; that of "coming by chance, unintentional" is from 1570s. Accidential (1811) sometimes serves now in the sense "characterized by non-essential qualities" and goes with accidence.

late 14c., "non-essential quality," from accidental (adj.). The musical sense is from 1868; so called because they alter the note without essentially changing the key of the passage.

late 14c., "fulfill, perform, carry out an undertaking," from Old French acompliss-, present-participle stem of acomplir "to fulfill, fill up, complete" (12c., Modern French accomplir), from Vulgar Latin *accomplere, from Latin ad "to" (see ad-) + complere "to fill up," transferred to "fulfill, finish (a task)," from com-, here probably as an intensive prefix (see com-), + plere "to fill" (from PIE root *pele- (1) "to fill"). Related: Accomplished; accomplishing.

late 14c., "completed, finished," past-participle adjective from accomplish (v.). From late 15c. as "perfect in acquirements as a result of training," from accomplish in an archaic sense "make complete by providing education in what is wanting," especially mental accomplishments and social graces.

"reckoning of numbers," late 14c., verbal noun from account (v.). From 1855 as "management of financial affairs." Phrase no accounting for tastes (1823) translates Latin de gustibus non est disputandum, from account (v.) in the "give an explanation" sense.

late 14c., accusacioun, "charge of wrongdoing," from Old French acusacion "charge, indictment" (Modern French accusation) or directly from Latin accusationem (nominative accusatio) "formal complaint, indictment," noun of action from past-participle stem of accusare "call to account, make complaint against," from ad causa, from ad "with regard to" (see ad-) + causa "a cause; a lawsuit" (see cause (n.)). The meaning "that which is charged (against someone)" is from early 15c.

late 14c., name of the potter's field near Jerusalem that was purchased with the money Judas Iscariot took to betray Jesus, literally "place of bloodshed," from Greek Akeldama, rendering an Aramaic (Semitic) name akin to Syriac haqal dema "the field of blood." So called for being purchased with the blood-money.

late 14c., adquisicioun, "act of obtaining," from Old French acquisicion "purchase, acquirement" (13c., Modern French acquisition) or directly from Latin acquisitionem (nominative acquisitio), noun of action from past-participle stem of acquirere "get in addition, accumulate," from ad "to," here perhaps emphatic (see ad-), + quaerere "to seek to obtain" (see query (v.)).

The meaning "thing obtained" is from late 15c. The vowel change of -ae- to -i- in Latin is due to a phonetic rule in that language involving unaccented syllables in compounds.