Online Etymology Dictionary

D: from Gk. delta, from Phoenician and Hebrew daleth. The sign for "500" in Roman numerals. 3-D is attested from 1953.
D-day: 1918, "date set for the beginning of a military operation," with D as an abbreviation of day, cf. H-hour, also from the same military order of Sept. 7, 1918:
"The First Army will attack at H-Hour on D-Day with the object of forcing the evacuation of the St. Mihiel salient." [Field Order No. 8, First Army, A.E.F.]
"They designate the day and hour of the operation when the day and hour have not yet been determined, or where secrecy is essential" [U.S. Army Center of Military History Web site]. Now almost exclusively of June 6, 1944.
D.A.: Amer.Eng., acronym for district attorney from 1934; for duck's ass haircut (or, as OED would have it, duck's arse), from 1951. So called for the shape of it at the back of the head.
d.c.: abbreviation of direct current, attested from 1898.
D.C.: abbreviation of District of Columbia, apparently not widely used before 1820, but eventually it became necessary to distinguish it from the many other Washingtons in America. The city and the district (then known as Territory of Columbia) were named 1791; the territory was organized as a "district" in 1801, but the towns within it (Washington, Georgetown, Alexandria) remained separate municipalities and at one time all took D.C. The district was effectively organized as a unitary municipality in 1871.
D.D.: 1630, abbreviation of L. Divinitatis Doctor "Doctor of Divinity."
D.D.T.: also DDT, 1943, from dichlorodiphenyltrichlorethane; first made in U.S. by Geigey & Co.
D.T.: abbreviation of delirium tremens (q.v.), attested from 1858.
dab: c.1300, "heavy blow with a weapon," from dabben "to strike," perhaps imitative. Modern sense of "strike with a slight, quick pressure" developed by 1590s, infl. by Fr. dauber (see daub). Dab hand is British slang, 1828, from dab "expert" (1691), said to be school slang, of unknown origin.
dabble: 1550s, frequentative of dab. Original meaning was "wet by splashing;" modern fig. sense first recorded 1625.
dace: small, freshwater fish, early 15c., from O.Fr. darz, nom. or pl. of dart "dart" (see dart). So called for its movements.
Dachau: town in Bavaria, Germany, from O.H.G. daha "clay" + ouwa "island," describing its situation on high ground by the Amper River. Infamous as the site of a Nazi concentration camp nearby, opened in 1933 as a detention site for political prisoners and surrendered to the U.S. Army April 29, 1945. Not a death camp per se, but as it was one of the places where inmates from other camps were sent as the Reich collapsed at the end of the war, and as it was one of the few large camps overrun by the British or American forces, it has come to symbolize Nazi atrocities in many minds in the West. "Arbeit Macht Frei" was spelled out in metal on the gate (as it was on other concentration camps, e.g. Gross-Rosen, Sachsenhausen, Theresienstadt).
dachshund: 1881, from Ger. Dachshund, from Dachs, from common I.E. word for "badger" (cf. L. taxus, taxo) + Hund "dog." Probably so called because the dogs were used in badger hunts, their long, thin bodies bred to burrow into setts.
Dacron: 1951, proprietary name (reg. U.S. Patent Office) by E.I. du Pont de Nemours & Co.; an invented word, on the model of nylon, etc.
dactyl: late 14c., from Gk. dactylos "finger," of unknown origin; the metrical use (a long syllable followed by two short ones) is by analogy with the three joints of a finger.
dactylic: 1580s, from L. dactylicus, from Gk. daktylikos, from daktylos (see dactyl).
dad: recorded from c.1500, but probably much older, from child's speech, nearly universal and probably prehistoric (cf. Welsh tad, Ir. daid, Czech, L., Gk. tata, Lith. tete, Skt. tatah all of the same meaning).
dada: 1920, from Fr. dada "hobbyhorse," child's nonsense word, selected 1916 by Romanian poet Tristan Tzara, leader of the movement, for its resemblance to meaningless babble.
"Freedom: DADA DADA DADA, the howl of clashing colors, the intertwining of all contradictions, grotesqueries, trivialities: LIFE." [T. Tzara, "Dada Manifesto," 1918]
daddy: c.1500, colloquial dim. of dad. Daddylonglegs is from 1814; daddy-o is first recorded 1949, from bop talk.
dado: 1660s, of pedestals, from It. dado "die, cube," from L. datum (see die (n.)). Of wood panelling in a room, from 1787.
DAE: the usual acronym for "A Dictionary of American English on Historical Principles," published in four volumes between 1936 and 1944, edited by Sir William A. Craigie and James R. Hulbert.
daedal (adj.): 1580s, "skillful, cunning," from L. daedalus, from Gk. daidalos "skillful, cunningly wrought." Also an Anglicized form of the name Daedalus from Gk. mythology (1610s).
Daedalus: from Gk. Daidalos, lit. "the cunning worker," from daidallein "to work artfully."
daemon: alt. spelling (in specialized senses) of demon (q.v.).
daffodil: 154os, variant of M.E. affodill "asphodel," from M.L. affodillus, from L. asphodelus, from Gk. asphodelos, of unknown origin. The initial d- is perhaps from merging of the article in Du. de affodil, the Netherlands being a source for bulbs. First reference to the flower we know by this name (Narcissus pseudo-Narcissus) is from 1590s.
daffy: 1884, perhaps from daft (q.v.), or from obs. daffe "halfwit" (cf. 15c. daffish), of unknown origin.
daft: O.E. gedæfte "gentle, becoming," from P.Gmc. *gadaftjaz. Sense progression from "mildness" to "dullness" (14c.) to "foolish" (15c.) to "crazy" (1530s), probably influenced by analogy with daffe "halfwit."
dag: "thin rain, drizzle, wet fog," late 17c., from a Norse source, cf. O.N. dögg, pl. daggir "dew," from P.Gmc. *daowo- (cf. O.E. deaw; see dew).
dagga: "marijuana," 1660s, from Afrikaans, from Hottentot dachab "cannabis sativa smoked as a narcotic."
dagger: late 14c., apparently from O.Fr. dague "dagger," from O.Prov. dague, of uncertain origin, perhaps from V.L. *daca "Dacian knife," from the Roman province in modern Romania. The ending is possibly the faintly pejorative -ard suffix. Attested earlier (1279) as a surname (Dagard, presumably "one who carried a dagger").
dago: 1823, from Sp. Diego "James," orig. used of Sp. or Port. sailors on Eng. or Amer. ships, by 1900 it had broadened to include non-sailors and shifted to mean chiefly "Italian."
daguerreotype: 1839, from Fr., coined from name of inventor, Louis Daguerre.
dahlia: 1804, named 1791 for Anders Dahl (1751-1789), Swedish botanist who discovered it in Mexico. No blue variety had ever been cultivated, hence "blue dahlia," fig. for "something impossible or unattainable" (1880).
daily: O.E. dæglic (see day). This form is known from compounds, twadæglic "happening once in two days," þreodæglic "happening once in three days;" the more usual O.E. word was dæghwamlic.
daimon: transliteration of Gk. daimon "lesser god, guiding spirit, tutelary deity," 1852; see demon. Employed to avoid the post-classical associations of that word.
daimyo: also daimio, former title of the chief nobles of Japan, 1839, from Japanese, lit. "big name," from Chinese dai "great" + mio, myo "name.
dainty: early 13c., from O.Fr. daintie (n.) "price, value," also "delicacy, pleasure," from L. dignitatem (nom. dignitas) "worthiness, worth, beauty," from dignus "worthy" (see dignity). Adj. use first recorded c.1300. Meaning evolved from "choice, excellent," to "delicately pretty."
daiquiri: "type of alcoholic drink," 1920 (first recorded in F. Scott Fitzgerald), from Daiquiri, name of a district or village in eastern Cuba.
dairy: late 13c., from Anglo-Fr. -erie suffix affixed to M.E. daie (in daie maid "dairymaid"), from O.E. dæge "kneader of bread, housekeeper, female servant" (see dey (1)). The native word was dey-house.
dais: mid-13c., from Anglo-Fr. deis, from O.Fr. dais "table, platform," from L. discus "disk-shaped object," also, by medieval times, "table," from Gk. diskos "quoit, disk, dish." Died out in Eng. c.1600, preserved in Scotland, revived 19c. by antiquarians.
daisy: O.E. dægesege, from dæges eage "day's eye," because the petals open at dawn and close at dusk. In M.L. it was solis oculus "sun's eye." Daisy-cutter first attested 1791, originally of horses that trotted with low steps; later of cricket (1889) and baseball hits that skim along the ground. Daisy-chain in the "group sex" sense is attested from 1941. Pushing up daisies "dead" is attested from 1918, but variant with the same meaning go back to 1842.
Dakota: 1809, name of a group of native peoples from the Plains states speaking a Siouan language, from Dakota dakhota "friendly" (the name often is translated as "allies"). Recorded by Lewis and Clark (1804) as Dar co tar; in western dialects of the Teton subgroup, Lakota, Lakhota; in Assiniboine dialect, Nakota, Nakhota.
dal: 1690s, from Hindi dal "split pulse," from Skt. dala, from dal "to split."
dale: O.E. dæl, from P.Gmc. *dalan "valley," preserved from extinction in north of England by Norse infl. Akin to words for "bow" (v.), probably through the notion of a bend in the ground.
daliance: mid-14c., "confab, chat," from dally; probably formed in Anglo-Fr., but not attested there. Meaning "Amorous play, flirtation" is from late 14c.; that of "idle or frivolous activity" is from 1540s.
Dallas: city in Texas, U.S., settled 1841, named 1846 for George M. Dallas (1792-1864), U.S. vice president under Polk (1845-49); the family name (13c.) is from the barony of Dallas (Moray) or meaning "dweller at the house in the dale."
dally: c.1300, possibly from Anglo-Fr. dalier "to amuse oneself," of uncertain origin.
Dalmatia: region along the eastern Adriatic coast in what is now Croatia; perhaps from a derivative of PIE *dhal- "to bloom," in a sense of "young animal," in ref. to the mountain pastures.
Dalmatian: 1810, spotted dog, presumably named for Dalmatia, the reach of modern Croatia along the Adriatic coast, but dog breeders argue over whether there is a Croatian ancestry for the breed, which seems to be represented in Egyptian bas-reliefs and Hellenic friezes. Popular in early 1800s as a carriage dog, to trot alongside carriages and guard them in owner's absence. Even fire departments nowadays tend to spell it *Dalmation.
Dalton: in reference to a system of school education designed by Helen Parkhurst, 1920, from Dalton, Massachusetts, U.S., where it was first adopted.