Online Etymology Dictionary

datum (n.): proper Latin singular of data (q.v.).
daub (v.): late 14c. (Dauber as a surname is recorded from mid-13c.), from Old French dauber "to whitewash, plaster" (13c.), perhaps from Latin dealbare, from de- "thoroughly" + albare "to whiten," from albus "white" (see alb). Painting sense is from 1620s. Related: Daubed; daubing. As a noun, from mid-15c.
daughter (n.): Old English dohtor, from Proto-Germanic *dokhter, earlier *dhukter (source also of Old Saxon dohtar, Old Norse dottir, Old Frisian and Dutch dochter, German Tochter, Gothic dauhtar), from PIE *dhugheter (source also of Sanskrit duhitar-, Avestan dugeda-, Armenian dustr, Old Church Slavonic dušti, Lithuanian dukte, Greek thygater). The common Indo-European word, lost in Celtic and Latin (Latin filia "daughter" is fem. of filius "son"). The modern spelling evolved 16c. in southern England. Daughter-in-law is attested from late 14c.
daunt (v.): c. 1300, "to vanquish," from Old French danter, variant of donter (12c., Modern French dompter) "be afraid of, fear, doubt; control, restrain," from Latin domitare, frequentative of domare "to tame" (see tame (v.)). Sense of "to intimidate" is from late 15c. Related: Daunted; daunting.
dauntless (adj.): 1590s, from daunt + -less. Related: Dauntlessly.
dauphin (n.): "eldest son of the king of France" (title in use from 1349-1830), early 15c., from Middle French dauphin, literally "dolphin" (see dolphin).

Originally the title attached to "the Dauphin of Viennois," whose province (in the French Alps north of Provence) came to be known as Dauphiné. Three dolphins were on the coat of arms of the lords of Viennois, first worn by Guido IV (d.1142). It is said originally to have been a personal name among the lords of Viennois. Humbert III, the last lord of Dauphiné, ceded the province to Philip of Valois in 1349, on condition that the title be perpetuated by the eldest son of the king of France. The French fem. form is dauphine.
davenport (n.): "large upholstered couch," 1897, apparently named for the manufacturer. Earlier (1853) "a kind of small ornamental writing table." The proper name is attested from 12c., from a place in Cheshire (Old English Devennport).
David: masc. proper name, in Old Testament second king of Israel and Judah and author of psalms, from Hebrew Dawidh, literally "darling, beloved friend." The name was common in England and Scotland by 12c., but much earlier in Wales. A nickname form was Dawe, hence surnames Dawson, Dawkins. A top 10 list name for boys born in the U.S. from 1934 to 1992.
Davis Cup: donated 1900 as a national tennis championship trophy by U.S. statesman Dwight Filley Davis (1879-1945) while still an undergraduate at Harvard.
davit (n.): also david, "crane-like structure used to lower things off a ship, etc.," late 15c., apparently a use of the masc. proper name David on the pattern of applying common Christian names to useful devices (compare jack, jenny, jimmy).
Davy Jones: "the spirit of the sea," 1751, first mentioned in Smollett's "The Adventures of Peregrin Pickle" (chapter 15) as an ominous and terrifying fiend who "presides over all the evil spirits of the deep, and is often seen in various shapes, perching among the rigging on the eve of hurricanes, shipwrecks and other disasters." Davy Jones's Locker "bottom of the sea," is 1803, from nautical slang, of unknown origin; second element may be from biblical Jonah, regarded as unlucky by sailors.
daw (n.): early 15c., from Proto-Germanic *dakhwo (source also of Old High German taha, German Dohle), perhaps imitative of bird's cry. Medieval Latin tacula, Italian taccola are said to be Germanic loan words.
dawdle (v.): 1650s, perhaps a variant of daddle "to walk unsteadily." Perhaps influenced by daw, because the bird was regarded as sluggish and silly. Not in general use until c. 1775. Related: Dawdled; dawdling.
dawg (n.): colloquial for dog, attested from 1898.
dawn (v.): c. 1200, dauen, "to dawn, grow light," shortened or back-formed from dauinge, dauing "period between darkness and sunrise," (c. 1200), from Old English dagung, from dagian "to become day," from Proto-Germanic *dagaz "day" (source also of German tagen "to dawn;" see day (n.)). Probably influenced by Scandinavian cognates (Danish dagning, Old Norse dagan "a dawning"). Related: Dawned; dawning.
dawn (n.): 1590s, from dawn (v.).
day (n.): Old English dæg "day," also "lifetime," from Proto-Germanic *dagaz "day" (source also of Old Saxon, Middle Dutch, Dutch dag, Old Frisian dei, Old High German tag, German Tag, Old Norse dagr, Gothic dags), according to Watkins, from PIE *agh- (2) "a day" considered as a span of time. He adds that the Germanic initial d- is "of obscure origin."

Not considered to be related to Latin dies (see diurnal), but rather to Sanskrit dah "to burn," Lithuanian dagas "hot season," Old Prussian dagis "summer." Meaning originally, in English, "the daylight hours;" expanded to mean "the 24-hour period" in late Anglo-Saxon times. The day formerly began at sunset, hence Old English Wodnesniht was what we would call "Tuesday night." Names of the weekdays were not regularly capitalized in English until 17c. Day off first recorded 1883; day-tripper first recorded 1897. The days in nowadays, etc. is a relic of the Old English and Middle English use of the adverbial genitive.
day care (n.): also daycare, day-care, 1964, from day + care (n.).
Day-Glo: 1951, proprietary name (Dane & Co. of London) for a brand of fluorescent paint.
daybreak (n.): 1520s, from day + break (n.).
daydream (n.): 1680s, from day + dream (n.). As a verb, attested from 1820. Related: Daydreamer; daydreaming.
daylight (n.): c. 1300 (as two words from mid-12c., daies liht), from day + light (n.); its figurative sense of "clearly visible open space between two things" (1820) has been used in references to boats in a race, U.S. football running backs avoiding opposing tackles, a rider and a saddle, and the rim of a glass and the surface of the liquor. The (living) daylights that you beat out of someone were originally slang for "the eyes" (1752), extended figuratively to the vital senses.
daylong (adj.): Old English dæglang; see day + long (adj.).
daytime (n.): 1530s, from day + time (n.).
daze (v.): early 14c., dasen, perhaps from Old Norse *dasa (compare dasask "to become weary," with reflexive suffix -sk). Or perhaps from Middle Dutch dasen "act silly." Perhaps originally "to make weary with cold," which is the sense of Icelandic dasask (from the Old Norse word). Related: Dazed.
daze (n.): "a dazed condition," 1825, from daze (v.).
dazzle (v.): late 15c., frequentative of Middle English dasen (see daze (v.)). Originally intransitive; the transitive sense is from 1530s. Related: Dazzled; dazzling.
de: Latin adverb and preposition of separation in space, meaning "down from, off, away from," and figuratively "concerning, by reason of, according to;" from PIE demonstrative stem *de- (see to).
de facto: Latin, literally "in fact, in reality," thus, "existing, but not necessarily legally ordained;" from facto, ablative of factum "deed, act" (see fact).
de jure: Latin, literally "of law," thus "legitimate, lawful, by right of law, required by law." Jure is ablative of ius "law" (see just (adj.)).
de minimis: Latin, literally "of little things," thus, "so minor as to not be worth regarding."
de novo: Latin, literally "anew, afresh."
de profundis: the 130th Psalm, so called for its opening words, Latin, literally "out of the depths."
de rigueur: 1849, French, literally "of strictness," thus "according to obligation of convention." See rigor.
de-: active word-forming element in English and in many words inherited from French and Latin, from Latin de "down, down from, from, off; concerning" (see de), also used as a prefix in Latin usually meaning "down, off, away, from among, down from," but also "down to the bottom, totally" hence "completely" (intensive or completive), which is its sense in many English words. As a Latin prefix it also had the function of undoing or reversing a verb's action, and hence it came to be used as a pure privative -- "not, do the opposite of, undo" -- which is its primary function as a living prefix in English, as in defrost (1895), defuse (1943), etc. Compare also dis-.
de-emphasize (v.): also deemphasize, 1938, from de- + emphasize. Related: De-emphasized; de-emphasizing.
de-escalate (v.): also deescalate, 1964, from de- + escalate. Related: De-escalated; de-escalating; de-escalation.
deacon (n.): Old English deacon, diacon, from Late Latin diaconus, from Greek diakonos "servant of the church, religious official," literally "servant," from dia- "thoroughly" + PIE *kon-o-, from root *ken- (1) "to set oneself in motion."
deactivate (v.): 1904, from de- + activate. Related: Deactivated; deactivating; deactivation.
dead (adj.): Old English dead "dead," also "torpid, dull;" of water, "still, standing," from Proto-Germanic *daudaz (source also of Old Saxon dod, Danish død, Swedish död, Old Frisian dad, Middle Dutch doot, Dutch dood, Old High German tot, German tot, Old Norse dauðr, Gothic dauþs "dead"), from PIE *dhou-toz-, from root *dheu- (3) "to die" (see die (v.)).

Meaning "insensible" is first attested early 13c. Of places, "inactive, dull," from 1580s. Used from 16c. in adjectival sense of "utter, absolute, quite" (as in dead drunk, first attested 1590s; dead heat, 1796). As an adverb, from late 14c. Dead on is 1889, from marksmanship. Dead duck is from 1844. Dead letter is from 1703, used of laws lacking force as well as uncollected mail. Phrase in the dead of the night first recorded 1540s. Dead soldier "emptied liquor bottle" is from 1913 in that form; the image is older.
dead end (n.): "closed end of a passage," 1886, from dead (adj.) + end (n.). Figurative use is attested from 1922. As an adjective, from 1928; as a verb, from 1921. Related: Deadender (by 1996).
dead man's hand (n.): in poker, pair of aces and pair of eights, supposedly what Wild Bill Hickock held when Jack McCall shot him in 1876.
dead reckoning (n.): "ascertaining the position of a ship by measurement of the distance run," 1610s, might be from nautical abbreviation ded. ("deduced") in log books, but it also fits dead (adj.) in the sense of "unrelieved, absolute."
Dead Sea: mid-13c., from dead (adj.) + sea; its water is 26 percent salt (as opposed to 3 or 4 percent in most oceans) and supports practically no life. In the Bible it was the "Salt Sea" (Hebrew yam hammelah), also "Sea of the Plain" and "East Sea." In Arabic it is al-bahr al-mayyit "Dead Sea." The ancient Greeks knew it as he Thalassa asphaltites "the Asphaltite Sea." Latin Mare Mortum, Greek he nekra thalassa (both "The Dead Sea") referred to the sea at the northern boundaries of Europe, the Arctic Ocean.
deadbeat (n.): "worthless sponging idler," 1863, American English slang, perhaps originally Civil War slang, from dead (adj.) + beat. Earlier used colloquially as an adjectival expression to mean "completely beaten" (1821), and perhaps the base notion is of "worn out, good for nothing." It is noted in a British source from 1861 as a term for "a pensioner."
In England "dead beat" means worn out, used up. ... But here, "dead beat" is used, as a substantive, to mean a scoundrel, a shiftless, swindling vagabond. We hear it said that such a man is a beat or a dead beat. The phrase thus used is not even good slang. It is neither humorous nor descriptive. There is not in it even a perversion of the sense of the words of which it is composed. Its origin is quite beyond conjecture. ["Americanisms," in "The Galaxy," January 1878]
It also was used of a kind of regulating mechanism in pendulum clocks.
deaden (v.): 1660s "deprive of or diminish (some quality)," from dead (adj.) + -en (1). Earlier the verb was simply dead. Related: Deadened; deadening.
Deadhead (n.): by 1974 in sense of "devotee of the rock music band the Grateful Dead;" earlier (with lower-case) "one who rides for free on the railroads" (1866), and "non-paying spectator" (1841).
deadline (n.): "time limit," 1920, American English newspaper jargon, from dead (adj.) + line (n.). Perhaps influenced by earlier use (1864) to mean the "do-not-cross" line in Civil War prisons, which figured in the Wirz trial.
And he, the said Wirz, still wickedly pursuing his evil purpose, did establish and cause to be designated within the prison enclosure containing said prisoners a "dead line," being a line around the inner face of the stockade or wall enclosing said prison and about twenty feet distant from and within said stockade; and so established said dead line, which was in many places an imaginary line, in many other places marked by insecure and shifting strips of [boards nailed] upon the tops of small and insecure stakes or posts, he, the said Wirz, instructed the prison guard stationed around the top of said stockade to fire upon and kill any of the prisoners aforesaid who might touch, fall upon, pass over or under across the said "dead line" .... ["Trial of Henry Wirz," Report of the Secretary of War, Oct. 31, 1865]
deadlock (n.): "complete standstill," from dead (adj.), in its emphatic use, + lock (n.). First attested 1779 in Sheridan's play "The Critic."
deadly (adj.): Old English deadlic "mortal, subject to death," also "causing death;" see dead + -ly (1). Meaning "having the capacity to kill" is from late 14c. (Old English words for this included deaðbærlic, deaðberende).