dun (adj.) Look up dun at Dictionary.com
Old English dunn "dingy brown, dark-colored," perhaps from Celtic (compare Old Irish donn "dark;" Gaelic donn "brown, dark;" Welsh dwnn "brownish"), from PIE *donnos, *dusnos "dark."
Duncan Look up Duncan at Dictionary.com
from Gaelic donn "brown, dark" (see dun (adj.)) + ceann "head."
dunce (n.) Look up dunce at Dictionary.com
"dullard," 1570s, from earlier Duns disciple "follower of John Duns Scotus" (c.1265-1308), Scottish scholar of philosophy and theology supposed to have been born at Duns in Berwickshire. By 16c., humanist reaction against medieval theology singled him out as the type of the hairsplitting scholastic. It became a general term of reproach applied to more conservative philosophical opponents by 1520s, later extended to any dull-witted student.
dunderhead (n.) Look up dunderhead at Dictionary.com
1620s, from head (n.); the first element is obscure; perhaps from Middle Dutch doner, donder "to thunder" (compare blunderbuss).
dundrearies (n.) Look up dundrearies at Dictionary.com
1867, long, flowing whiskers, like those worn by actor E.A. Sothern (1826-1881) while playing Lord Dundreary, witless, indolent chief character in English dramatist Tom Taylor's play "Our American Cousin" (1858).
dune (n.) Look up dune at Dictionary.com
1790, from French, Middle Dutch or Middle Low German dune, all perhaps from Gaulish *dunom (thus related to down (n.2)). The French dune "sand hill" (13c.) is held by Diez to be an Old French borrowing from Dutch duin or some other Germanic source. Italian and Spanish duna are from French. Dune buggy attested by 1965.
dung (n.) Look up dung at Dictionary.com
Old English dung "manure, fertilizer," common Germanic (cognates: Old Frisian and Old Saxon dung "manure;" Old High German tunga "manuring," tung "underground room covered with manure;" German Dung; Old Norse dyngja "heap of manure, women's apartment; Swedish dynga "dung, muck;" Danish dynge "heap, mass, pile"), perhaps from a PIE *dhengh- "covering" (cognates: Lithuanian dengti "to cover," Old Irish dingim "I press").

The word recalls the ancient Germanic custom (reported by Tacitus) of covering underground shelters with manure to keep in warmth in winter. The meaning "animal excrement," whether used as fertilizer or not, is from late 13c.
The whole body of journeymen tailors is divided into two classes, denominated Flints and Dungs: the former work by the day and receive all equal wages; the latter work generally by the piece [1824].
Dung beetle attested by 1630s. In colloquial American English, tumble-bug. An Old English word for it was tordwifel "turd weevil."
dungaree Look up dungaree at Dictionary.com
1610s, dongerijns, from Hindi dungri "coarse calico," from the name of a village, now one of the quarters of Bombay.
dungarees (n.) Look up dungarees at Dictionary.com
trousers made of dungaree, 1868.
dungeon (n.) Look up dungeon at Dictionary.com
c.1300, "great tower of a castle," from Old French donjon "great tower of a castle" (12c.), from Gallo-Roman *dominionem, from Late Latin dominium, from Latin dominus "master" (of the castle; see domain). Sense of "castle keep" led to "strong (underground) cell" in English early 14c. The original sense went with the variant donjon.
dunghill (n.) Look up dunghill at Dictionary.com
early 14c., from dung + hill (n.).
dunk (v.) Look up dunk at Dictionary.com
1919, American English, from Pennsylvania German dunke "to dip," from Middle High German dunken, from Old High German dunkon, thunkon "to soak," from PIE root *teng- "to soak" (see tincture).

Basketball sense is first recorded 1937 as a verb, 1971 as a noun (earlier dunk shot). German-American Anabaptist sect of Dunkers (who baptize with triple immersion) first recorded by that name 1756.
Dunkirk Look up Dunkirk at Dictionary.com
city on the northeast coast of France, French dunkerque, literally "dune church," from Middle Dutch dune (see dune) + kerke (see church (n.)); in reference to the 7c. church of St. Eloi.
dunno (v.) Look up dunno at Dictionary.com
colloquial for "(I) don't know," first attested 1842 in American English.
duo (n.) Look up duo at Dictionary.com
1580s, "song for two voices," via either Italian or French, from Latin duo "two" (see two). Meaning "two people" (especially as an entertainment team) attested by 1887.
duodecimal (adj.) Look up duodecimal at Dictionary.com
1714, from Latin in duodecimo (see duodecimo).
duodecimo Look up duodecimo at Dictionary.com
1650s, from Latin in duodecimo (folded) "in a twelfth" of a sheet, from ablative of duodecimus "twelfth," from duodecim (see dozen). Often abbreviated 12mo.; a book in which each page is the twelfth part of the printer's sheet.
duodenal (adj.) Look up duodenal at Dictionary.com
1817; see duodenum + -al (1).
duodenum (n.) Look up duodenum at Dictionary.com
late 14c., from Medieval Latin duodenum digitorium "space of twelve digits," from Latin duodeni "twelve each." Coined by Gerard of Cremona (d.1187), who translated "Canon Avicennae," a loan-translation of Greek dodekadaktylon, literally "twelve fingers long," the intestine part so called by Greek physician Herophilus (c.353-280 B.C.E.) for its length, about equal to the breadth of twelve fingers.
dupe (n.) Look up dupe at Dictionary.com
1680s, from French dupe "deceived person," from Middle French duppe (early 15c.), thieves' jargon, perhaps from phrase de huppe "of the hoopoe," an extravagantly crested and reputedly stupid bird.
dupe (v.) Look up dupe at Dictionary.com
1704, from dupe (n.). Related: Duped; duping.
duplex (adj.) Look up duplex at Dictionary.com
1817, "composed of two parts," from Latin duplex, from duo "two" (see two) + -plex, from Greek plax (genitive plakos) "flat surface." The noun sense of "house for two families; two-story apartment" is American English, 1922.
duplicate (adj.) Look up duplicate at Dictionary.com
mid-15c., "having two parts, double," from Latin duplicatus, past participle of duplicare "to double," from duo "two" (see two) + plicare "to fold" see ply (v.1)). Meaning "exactly corresponding, that is an exact copy of" is from 1812.
duplicate (v.) Look up duplicate at Dictionary.com
1620s, "to double," from Latin duplicatus, past participle of duplicare (see duplicate (adj.)). Meaning "make an exact copy" is from 1640s (implied in duplicated). Related: Duplicating. The noun is first recorded 1530s.
duplication (n.) Look up duplication at Dictionary.com
early 15c., "doubling," from Middle French duplicacion (13c.) and directly from Latin duplicationem (nominative duplicatio), noun of action from past participle stem of duplicare (see duplicate (adj.)). Meaning "repetition" is from 1580s.
duplicative (adj.) Look up duplicative at Dictionary.com
1870; see duplicate (v.) + -ive.
duplicitous (adj.) Look up duplicitous at Dictionary.com
1831; see duplicity + -ous.
duplicity (n.) Look up duplicity at Dictionary.com
early 15c., from Old French duplicite (13c.), from Late Latin duplicitatem (nominative duplicitas) "doubleness," in Medieval Latin "ambiguity," noun of quality from duplex (genitive duplicis) "twofold." The notion is of being "double" in one's conduct (compare Greek diploos "treacherous, double-minded," literally "twofold, double").
dura mater (n.) Look up dura mater at Dictionary.com
"tough outer membrane surrounding the brain," c.1400, from Medieval Latin dura mater cerebri, literally "hard mother of the brain," a loan-translation of Arabic umm al-dimagh as-safiqa, literally "thick mother of the brain." "In Arabic, the words 'father,' 'mother,' and 'son' are often used to denote relationships between things" [Klein].
durability (n.) Look up durability at Dictionary.com
late 14c., from Old French durabilité, from Late Latin durabilitatem (nominative durabilitas), noun of quality from Latin durabilis (see durable).
durable (adj.) Look up durable at Dictionary.com
late 14c., from Old French durable (11c.), from Latin durabilis "lasting, permanent," from durare "to last, harden" (see endure). Durable goods attested from 1930.
durance (n.) Look up durance at Dictionary.com
late 15c., from Old French durance "duration," from durer "to endure," from Latin durare (see endure).
duration (n.) Look up duration at Dictionary.com
late 14c., from Old French duration, from Medieval Latin durationem (nominative duratio), noun of action from past participle stem of Latin durare "harden" (see endure). Old legalese phrase for the duration popularized 1916 in reference to British enlistments in World War I.
duress (n.) Look up duress at Dictionary.com
early 14c., "harsh or severe treatment," from Old French duresse, from Latin duritia "hardness," from durus "hard" (see endure). The Old French suffix -esse is from Latin -itia, added to adjectives to form nouns of quality (compare riches, largesse). Sense of "coercion, compulsion" is from 1590s.
Durham Look up Durham at Dictionary.com
c.1000, Dunholm "city on a hill," a merger of Old English dun "hill" (see down (n.2)) and Scandinavian holmr (see holm). The change from -n- to -r- is a result of Norman confusion (see Shrewsbury). As a breed of cattle, by 1810.
durian (n.) Look up durian at Dictionary.com
1580s, from Malay durian, from duri "thorn, prickle." So called for its rind.
during (prep.) Look up during at Dictionary.com
late 14c., durand, present participle of obsolete verb duren "to last, endure" (mid-13c.), from Old French durer, from Latin durare "endure" (see endure). During the day really is "while the day endures," and the usage is a transference into English of a Latin ablative absolute (compare durante bello "during (literally 'enduring') the war").
durst (v.) Look up durst at Dictionary.com
see dare (v.).
durum (n.) Look up durum at Dictionary.com
species of wheat, 1908, from Latin durum, neuter of durus "hard" (see endure). The seeds are tough.
Dushanbe Look up Dushanbe at Dictionary.com
capital of Tajikistan, from Tajik dushanbe "Monday" (a compound of du "two" + Shanbe "Saturday," literally "Sabbath;" thus "two days after Saturday"); so called in reference to a regular Monday market there. Known from 1929-1961 as Stalinabad.
dusk (n.) Look up dusk at Dictionary.com
c.1200, dosk "obscure, to become dark," perhaps from Old English dox "dark-haired, dark from the absence of light" (cognate with Swedish duska "be misty," Latin fuscus "dark," Sanskrit dhusarah "dust-colored;" also compare Old English dosan "chestnut-brown," Old High German tusin "pale yellow") with transposition of -k- and -s-, perhaps via a Northumbrian variant (compare colloquial ax for ask). But OED notes that "few of our words in -sk are of OE origin." A color word originally; the sense of "twilight" is recorded from 1620s.
dusky (adj.) Look up dusky at Dictionary.com
1550s, "somewhat dark," from dusk + -y (2). Related: Duskiness.
dust (n.) Look up dust at Dictionary.com
Old English dust, from Proto-Germanic *dunstaz (cognates: Old High German tunst "storm, breath," German Dunst "mist, vapor," Danish dyst "milldust," Dutch duist), from PIE *dheu- (1) "dust, smoke, vapor" (cognates: Sanskrit dhu- "shake," Latin fumus "smoke"). Meaning "that to which living matter decays" was in Old English, hence, figuratively, "mortal life."
dust (v.) Look up dust at Dictionary.com
c.1200, "to rise as dust;" later "to sprinkle with dust" (1590s) and "to rid of dust" (1560s); from dust (n.). Related: Dusted; dusting. Sense of "to kill" is U.S. slang first recorded 1938 (compare bite the dust under bite (v.)).
dust bowl Look up dust bowl at Dictionary.com
also dustbowl, "drought-plagued region of the U.S. Midwest," first recorded 1936.
dustbin (n.) Look up dustbin at Dictionary.com
1848, from dust (n.) + bin.
duster (n.) Look up duster at Dictionary.com
1570s, "dust brush for clothes," agent noun from dust (v.). Meaning "sifter" is from 1660s; that of "cloth worn to keep off dust" is from 1864.
dustup (n.) Look up dustup at Dictionary.com
"fight," 1897, from dust + up; perhaps from dust "confusion, disturbance" (1590s). To dust (someone's) coat was ironical for "to beat (someone) soundly" (1680s).
dusty (adj.) Look up dusty at Dictionary.com
early 13c., from dust + -y (2). Related: Dustiness.
dusty miller (n.) Look up dusty miller at Dictionary.com
common name for auricula, 1825, so called from the powder on the leaves and flower; millers, by the nature of their work, being famously dusty.