Online Etymology Dictionary

doth: see does.
dotty (adj.): 1812, "full of dots," from dot (n.) + -y (2). Meaning "silly" is from c.1400, in dotypolle "dotty poll" (i.e. "dotty head"), in which case the first element is from dote (v.).
Douai: or Douay, name of town in northern France, used elliptically in reference to the English translation of the Bible begun there late 16c., sanctioned by Roman Catholic Church. [Also called Rheims-Douai translation because it was published in Rheims in 1582]. It uses more Latinate words than the KJV.
double (adj.): early 13c., from Old French doble (10c.) "double, two-fold; two-faced, deceitful," from Latin duplus "twofold, twich as much" from duo "two" (see two) + -plus "more" (see plus). Double standard attested by 1951. Military double time (1833) originally was 130 steps per minute.
double (v.): late 13c., "make double," from Old French dobler, from Latin duplare, from duplus (see double (adj.)). Meaning "to work as, in addition to one's regular job" is c.1920, circus slang, from performers who also played in the band. Related: Doubled; doubling. To double up bodily is from 1814.
A blow on the stomach "doubles up" the boxer, and occasions that gasping and crowing which sufficiently indicate the cause of the injury .... [Donald Walker, "Defensive Exercises," 1840]
double (n.): mid-14c., "amount twice as great," also "duplicate copy," from double (adj.).
double agent (n.): 1935, from double (adj.) + agent (n.).
double date (v.): 1931, from double (adj.) + date (v.2).
Double Dutch: "gibberish," 1864 (High Dutch for "incomprehensible language" is recorded from 1789); from double (adj.) + Dutch.
double entendre: also double-entendre, 1670s, from French (where it was rare and is now obsolete), literally "a twofold meaning," from entendre (now entente) "to hear, to understand, to mean." The proper Modern French phrase would be double entente, but the phrase has become established in English in its old form.
double talk (n.): 1938, from double (adj.) + talk (n.).
double-check (v.): 1958, from double (adj.) + check (v.). Related: Double-checked; double-checking.
double-cross (n.): 1834, from double (adj.) + cross (n.) in the sense of "pre-arranged swindle or fix." Originally to win a race after promising to lose it. As a verb from 1903, American English. Related: Double-crossed; double-crossing.
double-decker (n.): 1835 of ships, 1867 of street vehicles; from double (adj.) + deck (n.).
double-header (n.): 1869, American English, originally a kind of fireworks or a railway train pulled by two engines; see double (adj.) + head (n.). Baseball sense is c.1890.
double-park (v.): 1931, from double (adj.) + park (v.). Related: Double-parked; double-parking.
double-take (n.): 1922, from double (adj.) + take (n.).
double-team (v.): "attack two-on-one," 1860; see double (adj.) + team (v.). Related: Double-teamed; double-teaming.
doublespeak (n.): 1957, from double (adj.) + speak, coined on model of doublethink in Orwell's "Nineteen Eighty-Four" (the language in that book was Newspeak).
doublet (n.): early 14c. as a type of men's garment, from Old French doublet (12c.), from diminutive of duble (see double (adj.)). From 1550s as "one of two things that are alike."
doublethink (n.): 1948, coined by Orwell in "Nineteen Eighty-Four," from double (adj.) + think.
doubloon (n.): 1620s, from French doublon (16c.) and directly from Spanish doblon a gold coin, augmentative of doble "double" (coin so called because it was worth twice as much as the Spanish gold pistole), from Latin duplus "double" (see double (adj.)). Also see -oon.
doubly (adv.): late 14c., from double (adj.) + -ly (2).
doubt (v.): early 13c., "to dread, fear," from Old French doter "doubt, be doubtful; be afraid," from Latin dubitare "to doubt, question, hesitate, waver in opinion" (related to dubius "uncertain;" see dubious), originally "to have to choose between two things."

The sense of "fear" developed in Old French and was passed on to English. Meaning "to be uncertain" is attested in English from c.1300. The -b- was restored 14c. by scribes in imitation of Latin. Replaced Old English tweogan (noun twynung), from tweon "two," on notion of "of two minds" or the choice of two implied in Latin dubitare (cf. German Zweifel "doubt," from zwei "two").
doubt (n.): early 13c., from Old French dote (11c.) "fear, dread; doubt," from doter (see doubt (v.)).
doubtful (adj.): late 14c., from doubt (n.) + -ful. Related: Doubtfully; doubtfulness.
doubtless: mid-14c. (adv.), mid-15c. (adj.), from doubt (n.) + -less. Related: Doubtlessly.
douche (n.): 1766, "jet of water," from French douche (16c.), from Italian doccia "shower," from docciare "to spray," from Latin ductionem "a leading," from ducere "to lead" (see duke (n.)). Meaning "vaginal cleansing" is from 1833. The verb is first attested 1838. Related: Douched; douching.
douchebag (n.): also douche-bag, douche bag, 1893, from douche + bag (n.). American English slang sense of "contemptible person" attested by 1967.
dough (n.): Old English dag "dough," from Proto-Germanic *daigaz "something kneaded" (cf. Old Norse deig, Swedish deg, Middle Dutch deech, Dutch deeg, Old High German teic, German Teig, Gothic daigs "dough"), from PIE *dheigh- "to build, to form, to knead" (cf. Sanskrit dehah "body," literally "that which is formed," dih- "to besmear;" Greek teikhos "wall;" Latin fingere "to form, fashion," figura "a shape, form, figure;" Gothic deigan "to smear;" Old Irish digen "firm, solid," originally "kneaded into a compact mass"). Meaning "money" is from 1851.
doughboy (n.): "U.S. soldier," 1865, said to have been in oral use from 1854, or from the Mexican-American War (1847), it is perhaps from resemblance of big buttons on old uniforms to biscuits of that name (1680s), but there are various other conjectures.
doughface (n.): contemptuous nickname in U.S. politics for Northern Democrats who worked in the interest of the South before the Civil War; it was taken to mean "man who allows himself to be moulded." The source is an 1820 speech by John Randolph of Roanoke, in the wake of the Missouri Compromise.
Randolph, mocking the northerners intimidated by the South, referred to a children's game in which the players daubed their faces with dough and then looked in a mirror and scared themselves. [Daniel Walker Howe, "What Hath God Wrought," 2007]
Mask of dough is recorded from 1809, and the same image Randolph used is attested in another context by 1833.
doughnut (n.): 1809, American English, from dough + nut. First recorded by Washington Irving, who described them as "balls of sweetened dough, fried in hog's fat, and called doughnuts, or olykoeks." Meaning "a driving in tight circles" is U.S. slang, 1981.
doughty (adj.): Old English dohtig "competent, good, valiant," from dyhtig "strong," related to dugan "to be fit, be able, be strong," and influenced by its past participle, dohte.

All from Proto-Germanic *duhtiz- (cf. Middle High German tühtec, German tüchtig, Middle Dutch duchtich), from PIE *dheugh- "to be fit, be of use, proper" (cf. German Tugend "virtue," Greek teukhein "to make ready," Irish dual "becoming, fit," Russian dužij "strong, robust"). Rare after 17c.; in deliberately archaic or mock-heroic use since c.1800. If it had survived, its modern form would be dighty.
Douglas: family name (late 12c.), later masc. personal name, from Gaelic Dubh glas "the dark water," name of a place in Lanarkshire. Douglas fir named for David Douglas (1798-1834), Scottish botanist who first recorded it in Pacific Northwest, 1825. Douglas scheme, Douglas plan, Douglassite, etc. refer to "social credit" economic model put forth by British engineer Maj. Clifford Hugh Douglas (1879-1952).
doula (n.): by 1980, from Greek doulos (fem. doule) "slave."
dour (adj.): mid-14c., "severe," from Scottish and northern England dialect, probably from Latin durus "hard" (see endure); sense of "gloomy, sullen" is late 15c.
douse (v.): 1550s, "to strike, punch," which is perhaps from Middle Dutch dossen "beat forcefully" or a similar Low German word.

Meaning "to strike a sail in haste" is recorded from 1620s; that of "to extinguish (a light)" is from 1785; perhaps influenced by dout (1520s), an obsolete contraction of do out (cf. doff, don). OED regards the meaning "to plunge into water, to throw water over" (c.1600) as a separate word, of unknown origin, though admitting there may be a connection of some sort. Related: Doused; dousing.
dove (n.): probably from Old English dufe- (found only in compounds), from Proto-Germanic *dubon (cf. Old Saxon duba, Old Norse dufa, Swedish duva, Middle Dutch duve, Dutch duif, Old High German tuba, German Taube, Gothic -dubo), perhaps related to words for "dive," in reference to its flight.

Originally applied to all pigeons, now mostly restricted to the turtle dove. A symbol of gentleness from early Christian times, also of the Holy Spirit (cf. Gen. viii:8-12), and of peace and deliverance from anxiety; political meaning "person who advocates peace" attested by 1917, from the Christian dove of peace.
dove (v.): past tense of dive (q.v.).
dovecote (n.): early 15c., from dove (n.) + cote.
Dover: port in Kent, Old English Dofras (c.700), from Latin Dubris (4c.), from British Celtic *Dubras "the waters." Named for the stream that flows nearby.
dovetail: late 16c. (n.), 1650s (v.), from dove (n.) + tail. So called from resemblance of shape in the tenon or mortise of the joints to that of the bird’s tailfeather display. Related: Dovetailed.
Dow Jones: short for Dow Jones Industrial Average, first published 1884 by Charles Henry Dow (1851-1902) and Edward D. Jones (1856-1920), later publishers of "The Wall Street Journal."
dowager (n.): 1520s, from Middle French douagere "widow with a dower" literally "pertaining to a dower," from douage "dower," from douer "endow," from Latin dotare, from dos (genitive dotis) "dowry" (see dowry).
dowdy: 1580s (n.), "an aukward, ill-dressed, inelegant woman" [Johnson]; 1670s (adj.), perhaps a diminutive of doue "poorly dressed woman" (early 14c.), of uncertain origin. The modern use of dowd (n.) is most likely a back-formation from dowdy. "If plaine or homely, wee saie she is a doudie or a slut" [Barnabe Riche, "Riche his Farewell to Militarie profession," 1581].
You don't have to be dowdy to be a Christian. [Tammy Faye Bakker, "Newsweek," June 8, 1987]
Related: Dowdily; dowdiness.
dowel (n.): mid-14c., dule "rim or section of a wheel," perhaps akin to Middle Low German dovel "plug, tap" (of a cask). Modern meaning is first attested 1794.
dower (n.): late 13c., from Old French doaire "dower, dowry, gift" (see dowry).
down (adv.): late Old English shortened form of Old English ofdune "downwards," from dune "from the hill," dative of dun "hill" (see down (n.2)). A sense development peculiar to English.

Used as a preposition since c.1500. Sense of "depressed mentally" is attested from c.1600. Slang sense of "aware, wide awake" is attested from 1812. Computer crash sense is from 1965. As a preposition from late 14c.; as an adjective from 1560s. Down-and-out is from 1889, American English, from situation of a beaten prizefighter. Down home (adj.) is 1931, American English; down the hatch as a toast is from 1931; down to the wire is 1901, from horse-racing. Down time is from 1952. Down under "Australia and New Zealand" attested from 1886; Down East "Maine" is from 1825.
down (n.1): "soft feathers," late 14c., from Old Norse dunn, perhaps ultimately from PIE root *dheu- (1) "to fly about (like dust), to rise in a cloud."