Online Etymology Dictionary

Danube: major river of Europe (German Donau, Hungarian Duna, Russian Dunaj), from Latin Danuvius, from Celtic *danu(w)-yo-, from PIE *danu- "river" (compare Don, Dnieper, Dniester).
Daoism (n.): alternative Romanization of Taoism (q.v.).
dap (n.): fist-bump greeting, with various theories as to origin and name meaning. In African-American popular culture by 1972 and controversial during the Vietnam War when used by U.S. soldiers, as it often was regarded by whites as a ritual act of black solidarity. Probably imitative (dap was used in 19c. for the bounce of a ball or the skip of a stone on water). Dap, meanwhile, is listed in the DAS as African-American vernacular c. 1950 for "aware, up to date," also "stylish, well-dressed," in the latter case at least a shortening of dapper.
Daphne: fem. proper name, from Greek daphne "laurel, bay tree;" in mythology the name of a nymph, daughter of the river Peneus, metamorphosed into a laurel by Gaia to save her from being ravished as she was pursued by Apollo.
dapper (adj.): mid-15c., "elegant," from Middle Dutch or Middle Low German dapper "bold, strong, sturdy," later "quick, nimble," from Proto-Germanic *dapraz, perhaps with ironical shift of meaning (source also of Old High German tapfar "heavy," German tapfer "brave"), from PIE root *dheb- "dense, firm, compressed."
dapple (v.): early 15c. (implied in past participle adjective dappled), perhaps from a Scandinavian source akin to Old Norse depill "spot," Norwegian dape "puddle." Perhaps a back-formation from, or merger with, Middle English adjective dapple-gray "apple-gray" (late 14c.), based on resemblance to the markings on an apple (compare Old Norse apalgrar "dapple-gray"), or, as it was used of gray horses with round blotches, perhaps via resemblance to apples themselves.
dar: Arabic word, literally "house," used in place names, such as Dar es Salaam, Tanzania, literally "House of Peace."
dare (v.): from first and third person singular of Old English durran "to brave danger, dare; venture, presume," from Proto-Germanic *ders- (source also of Old Norse dearr, Old High German giturran, Gothic gadaursan), from PIE *dhers- "to dare, be courageous" (source also of Sanskrit dadharsha "to be bold;" Old Persian darš- "to dare;" Greek thrasys "bold;" Old Church Slavonic druzate "to be bold, dare;" Lithuanian dristi "to dare," drasus "courageous").

An Old English irregular preterite-present verb: darr, dearst, dear were first, second and third person singular present indicative; mostly regularized 16c., though past tense dorste survived as durst, but is now dying, persisting mainly in northern English dialect. Meaning "to challenge or defy (someone)" is first recorded 1570s.
dare (n.): 1590s, from dare (v.).
daredevil (n.): 1794, "recklessly daring person," from dare (v.) + devil (n.). The devil might refer to the person, or the sense might be "one who dares the devil." Compare scarecrow, killjoy, pickpocket (n.), cutthroat, also fear-babe a 16c. word for "something that frightens children;" kill-devil "bad rum." As an adjective, from 1832.
Darfur: region in Sudan, named for its people, from Arabic dar, literally "house" + Fur, ethnic name of the indigenous African population.
daring (n.): late 14c., verbal noun from dare (v.).
Darius: name of three Persian rulers, notably Darius the Great, Persian emperor 521-485 B.C.E., from Greek Darius, from Old Persian Darayavaus, probably literally "he who holds firm the good," from PIE root *dher- (2) "to hold firmly, support" (see firm (adj.)).
Darjeeling: town in northeastern India, from Tibetan dojeling "diamond island," in reference to Vajrayana (literally "vehicle of the diamond") Buddhism. The "island" being the high ground of the place's site. As a type of tea, from 1882.
dark (adj.): Old English deorc "dark, obscure, gloomy; sad, cheerless; sinister, wicked," from Proto-Germanic *derkaz (source also of Old High German tarchanjan "to hide, conceal"). "Absence of light" especially at night is the original meaning. Application to colors is 16c. Theater slang for "closed" is from 1916.
dark (n.): early 13c., from dark (adj.). Figurative in the dark "ignorant" first recorded 1670s.
dark ages: 1739, any benighted time in history, period of ignorance; specific focus on the centuries from the fall of Rome to the revival of secular literature is from 1830s.
dark horse (n.): in politics, 1842, an image from horse racing, in which dark is used in its figurative sense of "unknown."
Moonraker is called a "dark horse"; that is neither his sire nor dam is known. ["Pierce Egan's Book of Sports," London, 1832]
darken (v.): c. 1300, "to make dark;" late 14c., "to become dark," from dark (adj.) + -en (1). The more usual verb in Middle English was simply dark, as it is in Chaucer and Shakespeare, and darken did not predominate until 17c. The Anglo-Saxons also had a verb sweorcan meaning "to grow dark." To darken someone's door (usually with a negative) is attested from 1729.
darkling (adv.): "in the dark," mid-15c., from dark (n.) + now-obsolete adverbial ending -ling (compare headlong).
But having nothing to do with the participial -ing it does not mean growing dark &c.; from the mistaken notion that it is a participle spring both the misuse of the word itself and the spurious verb darkle. [Fowler]
darkly (adv.): Old English deorclice "darkly, horribly, foully;" see dark + -ly (2).
darkness (n.): Old English deorcnysse, from dark + -ness. Figurative use is recorded from mid-14c. The 10c. Anglo-Saxon treatise on astronomy uses þeostrum for "darkness."
darky (n.): "black person" (now offensive), 1775, from dark (adj.) + -y (3). Related: Darkies.
darling (n.): Old English deorling "darling, favorite minion," double diminutive of deor "dear" (see dear (adj.)). The vowel shift from -e- to -a- (16c.) is usual for -er- followed by a consonant. "It is better to be An olde mans derlyng, than a yong mans werlyng" (1562).
darn (v.): "to mend" c. 1600, perhaps from Middle French darner "mend," from darne "piece," from Breton darn "piece, fragment, part." Alternative etymology is from obsolete dern (see dern). Related: Darned; darning.
darn (interj.): tame curse word, 1781, American English euphemism for damn, said to have originated in New England when swearing was a punishable offense; if so, its spread was probably influenced by 'tarnal, short for Eternal, as in By the Eternal (God), favorite exclamation of Andrew Jackson, among others (see tarnation). Related: darned (past participle adjective, 1806); darndest (superlative, 1844).
darnel (n.): weed growing in grainfields, c. 1300, from northern dialectal French darnelle; according to one theory the the second element is Old French neelle (Modern French nielle) "cockle," from Vulgar Latin nigella "black-seeded," from fem. of Latin nigellus "blackish."

But perhaps rather the word is related to Middle Dutch verdaernt, verdarnt "stunned, dumbfounded, angry," Walloon darne, derne "stunned, dazed, drunk," the plant being so called from its well-known inebriating quality (actually caused by fungus growing on the plant); the French word for it is ivraie, from Latin ebriacus "intoxicated," and the botanical name, Lolium temulentum, is from Latin temulent "drunken," though this sometimes is said to be "from the heavy seed heads lolling over under their own weight."
In some parts of continental Europe it appears the seeds of darnel have the reputation of causing intoxication in men, beasts, and birds, the effects being sometimes so violent as to produce convulsions. In Scotland the name of Sleepies, is applied to darnel, from the seeds causing narcotic effects. [Gouverneur Emerson, "The American Farmer's Encyclopedia," New York, 1860. It also mentions that "Haller speaks of them as communicating these properties to beer."]
dart (n.): early 14c., from Old French dart "throwing spear, arrow," from Proto-Germanic *darothuz source also of Old English daroð, Old High German tart, Old Norse darraþr "dart"). Italian and Spanish dardo are said to be from Germanic by way of Old Provençal.
dart (v.): late 14c., "to pierce with a dart," from dart (n.). Meaning "to move like a dart" is attested from 1610s. Related: Darted; darter; darting.
Darwin: surname attested from 12c., from Old English deorwine, literally "dear friend," probably used as a given name and also the source of the masc. proper name Derwin.
Darwinism (n.): 1864, from Charles Darwin (1809-1882), whose major works were "The Origin of Species" (1859) and "The Descent of Man" (1871), + -ism.
dash (v.): c. 1300, probably from a Scandinavian source (compare Swedish daska, Danish daske "to beat, strike"), somehow imitative. The oldest sense is that in dash to pieces and dashed hopes. Intransitive meaning "move quickly" appeared c. 1300, that of "to write hurriedly" is 1726. Related: Dashed; dashing.
dash (n.): late 14c., from dash (v.). Sporting sense is from 1881, originally "race run in one heat."
dashboard (n.): 1846, from dash (v.) + board (n.1); "board in front of a carriage to stop mud from being splashed ("dashed") into the vehicle by the horse's hoofs." Of motor vehicles, from 1904.
dashiki (n.): 1969, of West African origin.
dashing (adj.): 1801, "given to cutting a dash" (1786), which was a colloquial expression for "acting brilliantly," from dash (n.) in the sense of "showy appearance," which is attested from 1715. The sense of "splashing" is recorded from mid-15c.
dastard (n.): mid-15c., "one who is lazy or dull;" an English formation on a French model, probably from *dast, "dazed," past participle of dasen "to daze" (see daze (v.)) + deprecatory suffix -ard. Meaning "one who shirks from danger" is late 15c.
dastardly (adj.): 1560s, "showing despicable cowardice," originally "dull," from Middle English dastard + -ly (1).
dat: representing the pronunciation of that in West Indian, Irish, or African-American vernacular speech, from 1680s.
data (n.): 1640s, plural of datum, from Latin datum "(thing) given," neuter past participle of dare "to give" (see date (n.1)). Meaning "transmittable and storable computer information" first recorded 1946. Data processing is from 1954.
data base (n.): also database, attested from 1962, from data + base (n.).
date (n.1): "time," early 14c., from Old French date (13c.) "date, day; time," from Medieval Latin data, noun use of fem. singular of Latin datus "given," past participle of dare "to give, grant, offer," from PIE root *do- "to give" (source also of Sanskrit dadati "gives," danam "offering, present;" Old Persian dadatuv "let him give," Old Church Slavonic dati "give," dani "tribute;" Latin donum "gift;" Greek didomi, didonai, "to give, offer," doron "gift;" Lithuanian duonis "gift," Old Irish dan "gift, endowment, talent," Welsh dawn "gift").

The Roman convention of closing every article of correspondence by writing "given" and the day and month -- meaning perhaps "given to messenger" -- led to data becoming a term for "the time (and place) stated." (a Roman letter would include something along the lines of datum Romae pridie Kalendas Maias -- "given at Rome on the last day of April."
date (n.2): the fruit, late 13c., from Old French date, from Old Provençal datil, from Latin dactylus, from Greek daktylos "date," originally "finger, toe;" so called because of fancied resemblance between oblong fruit of the date palm and human digits. Possibly from a Semitic source (compare Hebrew deqel, Aramaic diqla, Arabic daqal "date palm") and assimilated to the Greek word for "finger."
date (n.3): "liaison," 1885, gradually evolving from date (n.1) in its general sense of "appointment;" romantic sense by 1890s. Meaning "person one has a date with" is from 1925.
date (v.2): "have a romantic liaison;" 1902, from date (n.3). Related: Dated; dating.
date (v.1): "to mark (a document) with the date," late 14c., from date (n.1). Meaning "to assign to or indicate a date" (of an event) is from c. 1400. Meaning "to mark as old-fashioned" is from 1895. Related: Dated; dating.
date rape (n.): by 1973, from date (n.3) + rape (n.1).
dated (adj.): "old-fashioned," 1900, past participle adjective from date (v.1).
dateline (n.): 1880, imaginary line down the Pacific Ocean on which the calendar day begins and ends, from date (n.1) + line (n.). Meaning "line of text that tells the date and place of origin of a newspaper, article, telegram, etc." is from 1888.
dative (adj.): mid-15c., from Latin dativus "pertaining to giving," from datus "given" (see date (n.1)); in grammatical use from Greek dotike (ptosis) "dative (case)," from dotikos "of giving nature," from dotos "given," from PIE root *do- "to give," from the same PIE root as the Latin word. In law, "that may be disposed of at pleasure," from 1530s. Typically the case of the indirect object, but sometimes also denoting "motion toward." In old Germanic languages, the "fourth case," catch-all for Indo-European dative, ablative, locative, and other cases.