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D 

fourth letter of the Roman alphabet, from Greek delta, from Phoenician and Hebrew daleth, pausal form of deleth "door," so called from its shape.

The form of the modern letter is the Greek delta (Δ) with one angle rounded. As the sign for "500" in Roman numerals, it is said to be half of CIƆ, which was an early form of M, the sign for "1,000." 3-D for "three-dimensional" is attested from 1952.

Unetymological -d- is the result of a tendency in English and neighboring languages, perhaps for euphony, to add -d- to -n-, and especially to insert or swap a -d- sound when -l- or -r- follow too closely an -n-.

Compare sound (n.1), gender (n.), thunder (n.), spindle, kindred, strand (n.2) "fiber of rope," dialectal rundel, rundle for runnel. Swound was a form of swoun (swoon) attested from mid-15c, and used by Malory, Spenser, Lyly, Middleton, Beaumont & Fletcher. Among the words from French are powder (n.), meddle, tender (adj.), remainder, also riband, jaundice. It is less evident in spider (an agent noun from the Germanic *spin- root), and perhaps explains lender in place of loaner.

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*da- 

*dā-, Proto-Indo-European root meaning "to divide."

It forms all or part of: betide; daimon; Damocles; deal (v.); deal (n.1) "part, portion;" demagogue; demiurge; democracy; demography; demon; demotic; dole; endemic; epidemic; eudaemonic; geodesic; geodesy; ordeal; pandemic; pandemonium; tidal; tide (n.) "rise and fall of the sea;" tidings; tidy; time; zeitgeist.

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit dati "cuts, divides;" Greek dēmos "people, land," perhaps literally "division of society," daiesthai "to divide;" Old Irish dam "troop, company;" Old English tid "point or portion of time," German Zeit "time."

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da (n.)

"father," by 1851, a nursery or provincial abbreviation of dad.

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D.A. 

American English initialism (acronym) for district attorney from 1934; for duck's ass haircut (or, as OED would have it, duck's arse), from 1951. The haircut so called for the shape at the back of the head.

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dab (v.)

early 14c., dabben "to strike," of unknown origin, perhaps imitative. Compare Old Norse dabba "to tap, slap." Modern sense of "strike gently with the hand, strike with a slight, quick pressure" developed by mid-16c., influenced by French dauber (see daub). Related: Dabbed; dabbing; dabber.

As a noun from c. 1300, "heavy blow with a weapon," later "gentle blow with the hand or some soft substance" (1755). Meaning "small lump or mass of something soft" is from 1749. Dab hand is British slang, 1828, from dab "expert, knowing or skillful person" (1690s), said by OED to be "school slang," of unknown origin, perhaps from dab in the "strike lightly" sense. Compare dabster, which meant both "an expert" (1708) or "a bungler" (1871, perhaps by confusion with daub).

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dabble (v.)

1550s, "to dip a little and often," hence "to wet by splashing," probably a frequentative of dab. Figurative sense of "do superficially" attested by 1620s. Related: Dabbled; dabbling. An Ellen Dablewife is in the Lancashire Inquests from 1336.

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dace (n.)

type of small European freshwater fish, mid-15c., also dars, dase, dare, from Old French darz "a dace," nominative or plural of dart "dart" (see dart (n.)). So called for its swiftness. Another theory traces it to a Medieval Latin darsus "a dart," which is said to be of Gaulish origin. Also used of similar or related fish. For loss of -r- before -s-, compare bass (n.1) from barse and see cuss (v.).

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dacha (n.)

Russian country house or small villa near a town, for summer use, 1896, from Russian dacha, originally "gift" (of land), from Slavic *datja, from PIE root *do- "to give."

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Dachau 

town in Bavaria, Germany, from Old High German 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, 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 British or American forces, in the West it came to symbolize Nazi atrocities. "Arbeit Macht Frei" was spelled out in metal on the gate (as it was on other camps, such as Gross-Rosen, Sachsenhausen, Theresienstadt).

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dachshund (n.)

breed of short-legged, long-bodied dogs, 1844, from German Dachshund (15c.), from Dachs "badger" (Old High German dahs, 11c., cognate with Middle Dutch das "badger"), from Proto-Germanic *thahsuz "badger," perhaps literally "builder, the animal that builds," in reference to its burrowing (from PIE root *teks- "to weave," also "to fabricate"), but according to Watkins "more likely" borrowed from the same PIE source as the Celtic totemic name *Tazgo- (source of Gaulish Tazgo-, Gaelic Tadhg), originally "badger."

Second element is German Hund "dog" (see hound (n.)). Probably so called because the dogs were used in badger hunts, their long, thin bodies bred to burrow into setts and draw the animal out. French taisson, Spanish texon, tejon, Italian tasso are Germanic loan words.

Within the last few years this little hound has been introduced into England, a few couple having been presented to the Queen, from Saxony. The dachshund is a long, low, and very strong hound, with full head and sweeping ears. The fore legs are somewhat bandy, and when digging their action is very mole-like. [John Henry Walsh, "The Dog in Health and Disease," London, 1859]
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