Online Etymology Dictionary

doo-wop: 1958, from the nonsense harmony phrases sung under the vocal lead (this one attested from mid-1950s).
doodad (n.): "unnamed thing," 1905, chiefly U.S., a made-up word (cf. doohickey).
doodah (n.): "excitement," 1915, from refrain of the minstrel song "Camptown Races."
doodle (v.): "scrawl aimlessly," 1935, from dialectal doodle, dudle "fritter away time, trifle," or associated with dawdle. It was a noun meaning "simple fellow" from 1620s.
LONGFELLOW: That's a name we made up back home for people who make foolish designs on paper when they're thinking. It's called doodling. Almost everybody's a doodler. Did you ever see a scratch pad in a telephone booth? People draw the most idiotic pictures when they're thinking. Dr. Von Holler, here, could probably think up a long name for it, because he doodles all the time. ["Mr. Deeds Goes to Town," screenplay by Robert Riskin, 1936; based on "Opera Hat," serialized in "American Magazine" beginning May 1935, by Clarence Aldington Kelland]
Related: Doodled; Doodling.
Doodle Sack. A bagpipe. Dutch. -- Also the private parts of a woman. ["Classical Dictionary of the Vulgar Tongue," 1796]
doodle-bug (n.): type of beetle or larvae, c.1866, Southern U.S. dialect; see doodle + bug (n.). The same word was applied 1944 in R.A.F. slang to German V-model flying bombs.
doofus (n.): student slang, "dolt, idiot, nerd," by 1960s. "Dictionary of American Slang" says "probably related to doo-doo and goofus."
doohickey (n.): also doohicky, a name for something one doesn't know the name of, 1914, American English, arbitrary formation.
doolally (adj.): "insane, eccentric," British slang, by 1917 in the armed services and in full doolally tap (with Urdu word for "fever"), from Deolali, near Bombay, India, which was a military camp (established 1861) with a large barracks and a chief staging point for British troops on their way to or from India; the reference is to men whose enlistments had expired who waited there impatiently for transport home.
doom (n.): Old English dom "law, judgment, condemnation," from Proto-Germanic *domaz (cf. Old Saxon and Old Frisian dom, Old Norse domr, Old High German tuom, Gothic doms "judgment, decree"), from PIE root *dhe- (cf. Sanskrit dhaman- "law," Greek themis "law," Lithuanian dome "attention"), literally "to set, put" (see factitious). A book of laws in Old English was a dombec. Modern sense of "fate, ruin, destruction" is c.1600, from the finality of the Christian Judgment Day.
doom (v.): late 14c., from doom (n.). Related: Doomed; dooming.
Doomsday (n.): Old English domes dæg, from domes, genitive of dom (see doom (n.)) + dæg "day" (see day (n.)).

In medieval England it was expected when the world's age reached 6,000 years from creation, which was thought to have been in 5200 B.C. Bede, c.720, complained of being pestered by rustici asking him how many years till the sixth millennium ended. There is no evidence for a general panic in the year 1000 C.E. Doomsday machine "bomb powerful enough to wipe out human life on earth" is from 1960.
door (n.): Middle English merger of Old English dor (neuter; plural doru) "large door, gate," and Old English duru (fem., plural dura) "door, gate, wicket;" both from Proto-Germanic *dur- (cf. Old Saxon duru, Old Norse dyrr, Danish dør, Old Frisian dure, Old High German turi, German Tür).

The Germanic words are from PIE *dhwer- "a doorway, a door, a gate" (cf. Greek thura, Latin foris, Gaulish doro "mouth," Gothic dauro "gate," Sanskrit dvárah "door, gate," Old Persian duvara- "door," Old Prussian dwaris "gate," Russian dver' "a door").

The base form is frequently in dual or plural, leading to speculation that houses of the original Indo-Europeans had doors with two swinging halves. Middle English had both dure and dor; form dore predominated by 16c., but was supplanted by door.
A door is what a dog is perpetually on the wrong side of. [Ogden Nash]
doorbell (n.): c.1815, from door + bell (n.).
doorknob (n.): 1847, American English, from door + knob.
doormat (n.): 1660s, from door + mat. Figurative use from 1861.
doorstep (n.): 1810, from door + step (n.).
doorway (n.): 1799, from door + way.
dooryard (n.): c.1764, American English, from door + yard (n.1).
doozy: also doozie, 1903 (adj.), 1916 (n.), perhaps an alteration of daisy, or from popular Italian actress Eleonora Duse (1859-1924). In either case, reinforced by Duesenberg, the expensive, classy make of automobile from the 1920s-30s.
dopamine: 1959, from DOPA, the amino acid (from first letter of elements of dioxyphenylalanine), + -amine.
dope (n.): 1807, American English, "sauce, gravy, thick liquid," from Dutch doop "thick dipping sauce," from doopen "to dip" (cf. dip (v.)). Extension to "drug" is 1889, from practice of smoking semi-liquid opium preparation. Meaning "foolish, stupid person" is older (1851) and may have a sense of "thick-headed." Sense of "inside information" (1901) may come from knowing before the race which horse had been drugged to influence performance. Dope-fiend is attested from 1896.
dope (v.): 1889, from dope (n.). Related: Doped; doping.
dopey (adj.): 1896, from dope (n.) + -y (2).
doppelganger (n.): 1830, from German Doppelgänger, literally "double-goer," originally with a ghostly sense. See double + gang (n.). Sometimes half-anglicized as doubleganger.
Doppler: 1871, in reference to Christian Doppler (1803-1853), Austrian scientist, who in 1842 explained the effect of relative motion on waves (originally to explain color changes in binary stars); proved by musicians performing on a moving train. Doppler shift is the change of frequency resulting from the Doppler effect.
Dora: fem. proper name, short for Dorothy, Dorothea.
Dorcas: fem. proper name, from Greek dorkas "gazelle, deer." Dorcas Society "ladies' meeting to make clothes for the poor" (1832) is from Acts ix:36-41.
Dorchester: Old English Dorcanceaster, earlier Dornwaraceaster, from Latin Durnovaria, from Romano-British *duro- "walled town."
dord (n.): 1934, a ghost word printed in "Webster's New International Dictionary" and defined as a noun used by physicists and chemists, meaning "density." In sorting out and separating abbreviations from words in preparing the dictionary's second edition, a card marked "D or d" meaning "density" somehow migrated from the "abbreviations" stack to the "words" stack. The "D or d" entry ended up being typeset as a word, dord, and defined as a synonym for density. The mistake was discovered in 1939.
Dorian (adj.): c.1600, in reference to the mode of ancient Greek music, literally "of Doris," from Greek Doris, district in central Greece, traditionally named for Doros, legendary ancestor of the Dorians, whose name is probably related to doron "gift" (see date (n.1)).
Doric (adj.): 1560s, see Dorian; in reference to the architectural order, 1610s. The Doric dialect in ancient Greek theater was broad and rustic, hence it has been applied in English to northern and Scots dialects (1837).
dork (n.): "stupid person," 1967, originally U.S. student slang, perhaps from earlier meaning "penis" (1964), itself probably an alteration of dick. Related: Dorky; dorkiness.
dorm (n.): 1900, colloquial shortening of dormitory.
dormancy (n.): 1789; see dormant + -cy.
dormant (adj.): late 14c., "fixed in place," from Old French dormant (12c.), present participle of dormir "to sleep," from Latin dormire "to sleep," from PIE root *drem- "to sleep" (cf. Old Church Slavonic dremati "to sleep, doze," Greek edrathon "I slept," Sanskrit drati "sleeps"). Meaning "in a resting situation" (in heraldry) is from c.1500. Meaning "sleeping' is from 1620s.
dormer (n.): 1590s, originally "window of a sleeping room," from Middle French dormeor "sleeping room," from dormir "to sleep" (see dormant).
dormitory (n.): mid-15c., from Latin dormitorium "sleeping place," from dormire "to sleep" (see dormant).
dormouse (n.): early 15c., possibly from Anglo-French *dormouse "tending to be dormant" (from stem of dormir "to sleep," see dormer), with the second element mistaken for mouse; or perhaps it is from a Middle English dialectal compound of mouse and Middle French dormir. The rodent is inactive in winter. French dormeuse, fem. of dormeur "sleeper" is attested only from 17c.
Dorothy: fem. proper name, from French Dorothée, from Latin Dorothea, from Greek, literally "gift of God," from doron "gift" (see date (n.1)) + fem. of theos "god" (see Thea). With the elements reversed, it becomes Theodora. The accessory called a Dorothy bag is so called from 1907.
dorsal (adj.): 1540s, from Middle French dorsal (14c.), from Late Latin dorsalis, corresponding to Latin dorsualis "of the back," from dorsum "back," of uncertain origin.
dory (n.1): "small, flat-bottomed boat," 1709, American English, perhaps from a West Indian or Central American Indian language.
dory (n.2): type of edible fish, mid-15c., from Old French doree, originally the fem. past participle of dorer "to gild," from Latin deauratus, from de- + aurare "to gild," from aurum (see aureate). So called in reference to its colorings.
dosage (n.): 1867; see dose + -age, perhaps on model of French dosage (1812).
dose (n.): c.1600, from Middle French dose (15c.), from Late Latin dosis, from Greek dosis "a portion prescribed," literally "a giving," used by Galen and other Greek physicians to mean an amount of medicine, from stem of didonai "to give" (see date (1)). Slang meaning "venereal disease" is from 1914.
dose (v.): 1650s, from dose (n.). Related: Dosed; dosing.
dossier (n.): 1880, from French dossier "bundle of papers," from dos "back" (12c.), supposedly because the bundle bore a label on the back, from Latin dossum, variant of dorsum "back." Or possibly from resemblance of the bulge in a mass of bundled papers to the curve of a back. Old French dossiere meant "back-strap, ridge strap (of a horse's harness)."
dot (n.): Old English dott "speck, head of a boil," perhaps related to Norwegian dot "lump, small knot," Dutch dot "knot, small bunch, wisp," Old High German tutta "nipple;" ultimate origin unclear.

Known from a single source c.1000; the word reappeared with modern meaning "mark" c.1530; not common until 18c. Morse telegraph sense is from 1838. On the dot "punctual" is 1909, in reference to a clock dial face. Dot-matrix first attested 1975.
dot (v.): 1740, from dot (n.). Related: Dotted; dotting.
dotage (n.): "the state of one who dotes," c.1300; see dote + -age. Originally of all sorts of mental impairment, not just that resulting from old age. First recorded late 14c. for "senility."
dotard (n.): "imbecile," late 14c., from dote + -ard.