Online Etymology Dictionary

deadpan: 1928, from dead (adj.) + pan (n.) in slang sense of "face."
deadweight (n.): 1650s, "weight of an inert body," from dead (adj.) + weight (n.).
deadwood (n.): 1887 in figurative sense of "useless person or thing," originally American English, from dead (adj.) + wood (n.). Dead wood in a forest is useful as firewood; perhaps the reference here is to the dried up parts of plants grown for commercial production of flowers or fruit.
deaf (adj.): Old English deaf "deaf," also "empty, barren," specialized from Proto-Germanic *daubaz (source also of Old Saxon dof, Old Norse daufr, Old Frisian daf, Dutch doof "deaf," German taub, Gothic daufs "deaf, insensate"), from PIE dheubh-, which was used to form words meaning "confusion, stupefaction, dizziness" (source also of Greek typhlos "blind," typhein "to make smoke;" Old English dumb "unable to speak;" Old High German tumb).

The word was pronounced to rhyme with reef until 18c. Deaf-mute is from 1837, after French sourd-muet. Deaf-mutes were sought after in 18c.-19c. Britain as fortune-tellers. Deaf as an adder (Old English) is from Psalms lviii:5.
deafen (v.): 1590s, "to make deaf," from deaf + -en (1). The earlier verb was simply deaf (mid-15c.). For "to become deaf, to grow deaf," Old English had adeafian (intransitive), which survived into Middle English as deave but then took on a transitive sense from mid-14c. and sank from use except in dialects (where it mostly has transitive and figurative senses), leaving English without an intransitive verb here.
deafening (adj.): "very loud," 1590s, from present participle of deafen (q.v.). Deafening silence is attested by 1830.
deafness (n.): late 14c., from deaf + -ness.
deal (n.1): from Old English dæl "part, share, quantity, amount," from Proto-Germanic *dailaz (source also of Old Norse deild, Old Frisian del, Dutch deel, Old High German and German teil, Gothic dails "part, share"), from PIE *dail- "to divide" (source also of Old Church Slavonic delu "part," Lithuanian dalis).

Business sense of "transaction, bargain" is 1837, originally slang. Meaning "an amount" is from 1560s. New Deal is from F.D. Roosevelt speech of July 1932. Big deal is 1928; ironic use first recorded 1951 in "Catcher in the Rye." Deal breaker is attested by 1975.
deal (n.2): "plank or board of pine," c. 1400, from Low German (compare Middle Low German dele), from Proto-Germanic *theljon, from PIE root *tel- "ground, floor." An Old English derivative was þelu "hewn wood, board, flooring."
deal (v.): Old English dælan "to divide, distribute, separate, share, bestow, dispense," from the source of deal (n.). Meaning "to distribute cards before a game" is from 1520s. To deal with "handle" is attested from mid-15c. Related: Dealt; dealing.
dealer (n.): Old English dælere "divider, distributor; agent, negotiator," agent noun from deal (v.). Meaning "player who passes out the cards in a game" is from c. 1600; meaning "one who deals in merchandise" is from 1610s. Illegal drug sense is recorded by 1920.
dealership (n.): 1916, from dealer + -ship.
dealt: past tense and past participle of deal (v.).
deamination (n.): 1912, from de- + amine + -ation.
dean (n.): early 14c., from Old French deien (12c., Modern French doyen), from Late Latin decanus "head of a group of 10 monks in a monastery," from earlier secular meaning "commander of 10 soldiers" (which was extended to civil administrators in the late empire), from Greek dekanos, from deka "ten" (see ten). Replaced Old English teoðingealdor. College sense is from 1570s (in Latin from late 13c.).
dear (adj.): Old English deore "precious, valuable, costly, loved, beloved," from Proto-Germanic *deurjaz (source also of Old Saxon diuri, Old Norse dyrr, Old Frisian diore, Middle Dutch dure, Dutch duur, Old High German tiuri, German teuer), further etymology unknown. Used interjectorily since 1690s. As a polite introductory word to letters, it is attested from mid-15c. As a noun, from late 14c., perhaps short for dear one, etc.
dearborn (n.): "light four-wheeled wagon," 1821, American English, supposedly from the name of the inventor, by tradition said to be Gen. Henry Dearborn (1751-1829).
dearly (adv.): Old English deorlice (see dear).
dearth (n.): mid-13c., derthe "scarcity" (originally used of famines, when food was costly because scarce; extended to other situations of scarcity from early 14c.), abstract noun formed from root of Old English deore "precious, costly" (see dear) + abstract noun suffix -th (2). Common Germanic formation, though not always with the same sense (cognates: Old Saxon diurtha "splendor, glory, love," Middle Dutch dierte, Dutch duurte, Old High German tiurida "glory").
deary (n.): also dearie, diminutive of dear with a notion of "dear one."
deasil (adj.): "rightwise, turned toward the right; motion according to the apparent course of the sun," 1771, from Gaelic deiseil, deiseal (adjective and adverb) "toward the south," taken in sense of "toward the right," from deas "right, right-hand; south," cognate with Irish deas, Old Irish dess, des, Welsh dehau, and ultimately with Latin dexter (see dexterity). The second element of the Gaelic word is not explained (one old guess, in the Century Dictionary (1902), is a proposed *iul "direction, guidance").
death (n.): Old English deað "death, dying, cause of death," in plura, "ghosts," from Proto-Germanic *dauthuz (source also of Old Saxon doth, Old Frisian dath, Dutch dood, Old High German tod, German Tod, Old Norse dauði, Danish død, Swedish död, Gothic dauþus "death"), from verbal stem *dheu- (3) "to die" (see die (v.)) + *-thuz suffix indicating "act, process, condition."
I would not that death should take me asleep. I would not have him meerly seise me, and onely declare me to be dead, but win me, and overcome me. When I must shipwrack, I would do it in a sea, where mine impotencie might have some excuse; not in a sullen weedy lake, where I could not have so much as exercise for my swimming. [John Donne, letter to Sir Henry Goodere, Sept. 1608]
Death's-head, a symbol of mortality, is from 1590s. Death row first recorded 1940s. Death knell is attested from 1814; death penalty from 1875; death rate from 1859. Slang be death on "be very good at" is from 1839. Death wish first recorded 1896. The death-watch beetle (1660s) inhabits houses, makes a ticking noise like a watch, and was superstitiously supposed to portend death.
FEW ears have escaped the noise of the death-watch, that is, the little clickling sound heard often in many rooms, somewhat resembling that of a watch; and this is conceived to be of an evil omen or prediction of some person's death: wherein notwithstanding there is nothing of rational presage or just cause of terror unto melancholy and meticulous heads. For this noise is made by a little sheathwinged grey insect, found often in wainscot benches and wood-work in the summer. [Browne, "Vulgar Errors"]
death camp (n.): 1944, in reference to the Nazis, probably translating German Todeslager; they also were known as extermination camps (German Vernichtungslager); historians usually count six of them: Auschwitz-Birkenau, Chełmno, Bełżec, Majdanek, Sobibór, Treblinka.
deathbed (n.): Old English, "the grave," from death (n.) + bed (n.). Meaning "bed on which someone dies" is from c. 1300.
deathless (adj.): 1580s, from death + -less. Related: Deathlessly; deathlessness.
deathly (adj.): Old English deaþlic "mortal" (see death). Meaning "deadly" is from late 12c.; that of "death-like" is from 1560s.
deb (n.): slang shortening of debutante, by 1920.
debacle (n.): "disaster," 1848, from French débâcle "downfall, collapse, disaster" (17c.), a figurative use, literally "breaking up (of ice on a river)," extended to the violent flood that follows when the river ice melts in spring; from débâcler "to free," from Middle French desbacler "to unbar," from des- "off" + bacler "to bar," from Vulgar Latin *bacculare, from Latin baculum "stick" (see bacillus). Sense of "disaster" was present in French before English borrowed the word.
debar (v.): early 15c., "to shut out, exclude," from French débarrer, from Old French desbarer (12c., which, however, meant only "to unbar, unbolt," the meaning turned around in French as the de- was felt in a different sense), from des- (see dis-) + barrer "to bar" (see bar (n.1)). Related: Debarment; debarred.
debark (v.): 1650s, from French débarquer (16c.), from de- (Old French des-; see dis-) + barque "bark" (see bark (n.2)).
debase (v.): 1560s, from de- "down" + base (adj.) "low," on analogy of abase (or, alternatively, from obsolete verb base "to abuse").
debatable (adj.): 1530s (late 15c. in Anglo-Latin), from Old French debatable (Modern French débattable), from debatre (see debate (v.)). Earliest references were to lands claimed by two nations; general sense is from 1580s.
debate (v.): late 14c., "to quarrel, dispute," also "discuss, deliberate upon the pros and cons of," from Old French debatre (13c., Modern French débattre), originally "to fight," from de- "down, completely" (see de-) + batre "to beat" (see battery). Related: Debated; debating.
debate (n.): early 14c., "a quarrel, dispute, disagreement," from Old French debat; see debate (v.). Sense of "a formal dispute, a debating contest" is perhaps from early 15c.
debauch (v.): 1590s, from Middle French débaucher "entice from work or duty," from Old French desbaucher "to lead astray," supposedly literally "to trim (wood) to make a beam" (from bauch "beam," from Frankish balk or some other Germanic source akin to English balk (n.)). A sense of "shaving" something away, perhaps, but the root is also said to be a word meaning "workshop," which gets toward the notion of "to lure someone off the job;" either way the sense evolution is unclear.
debauchee (n.): 1660s, from French débauché "debauched (person)," noun use of past participle of debaucher (see debauch).
Debauchee, n. One who has so earnestly pursued pleasure that he has had the misfortune to overtake it. [Ambrose Bierce, "Devil's Dictionary," 1911]
debauchery (n.): 1640s, from debauch + -ery. With a variety of spellings in 17c., such as debaush-, deboich-, debosh-.
debenture (n.): "written acknowledgment of a debt," early 15c., from Latin debentur "there are due" (said to have been the first word in formal certificates of indebtedness), passive present third person plural of debere "to owe" (see debt).
debilitate (v.): 1530s, from Latin debilitatus, past participle of debilitare "to weaken," from debilis "weak" (see debility). Related: Debilitated; debilitating.
debilitation (n.): early 15c., from French débilitation (13c.), from Latin debilitationem (nominative debilitas) "a laming, crippling, weakening," noun of action from past participle stem of debilitare "to weaken" (see debilitate).
debility (n.): early 15c., from Middle French debilite (Modern French débilité) or directly from Latin debilitatem (nominative debilitas) "a laming, crippling, weakening," from debilis "lame, disabled, crippled," figuratively "weak, helpless," from de- "from, away" (see de-) + -bilis "strength," from PIE root *bel- (see Bolshevik).
debit (n.): mid-15c., from Middle French debet or directly from Latin debitum "thing owed, that which is owing," neuter past participle of debere "to owe" (see debt). As a verb from 1680s. Debit card is attested from 1975.
debonair (adj.): c. 1200, "mild, gentle, kind courteous," from Old French debonaire, from de bon' aire "of good race," originally used of hawks, hence, "thoroughbred" (opposite of French demalaire). Used in Middle English to mean "docile, courteous," it became obsolete and was revived with an altered sense of "pleasant, affable" (1680s).
Deborah: fem. proper name, prophetess and judge in the Old Testament, Hebrew, literally "bee" (thus the name is the same as Melissa).
deboshed (adj.): 1590s, Englished spelling of French pronunciation of debauched "dissolute" (see debauch). Obsolete in England after mid-17c., retained in Scotland, and given a revival of sorts by Scott (1826), so that it turns up in 19c. literary works.
debridement (n.): "removal of damaged tissue from a wound," 1839, from French débridement, literally "an unbridling," from dé- (see de-) + bride "bridle," from a Germanic source akin to Middle High German bridel (see bridle). Related: debride, debriding.
debrief (v.): "obtain information (from someone) at the end of a mission," 1945, from de- + brief (v.). Related: Debriefed; debriefing.
debris (n.): 1708, from French débris "remains, waste, rubbish" (16c.), from obsolete debriser "break down, crush," from Old French de- (see de-) + briser "to break," from Late Latin brisare, possibly of Gaulish origin (compare Old Irish brissim "I break").
debt (n.): late 13c., dette, from Old French dete, from Latin debitum "thing owed," neuter past participle of debere "to owe," originally, "keep something away from someone," from de- "away" (see de-) + habere "to have" (see habit (n.)). Restored spelling after c. 1400. In Middle English, debt of the body (mid-14c.) was "that which spouses owe to each other, sexual intercourse."
debtor (n.): early 13c., dettur, dettour, from Old French detour, from Latin debitor "a debter," from past participle stem of debere; see debt. The -b- was restored in later French, and in English c. 1560-c. 1660. The KJV has detter three times, debter three times, debtor twice and debtour once.