Online Etymology Dictionary

delirious (adj.): 1703, from stem of delirium + -ous. Figurative use attested from 1791. Related: Deliriously.
delirium (n.): 1590s, from Latin delirium "madness," from deliriare "be crazy, rave," literally "go off the furrow," a plowing metaphor, from phrase de lire, from de "off, away" (see de-) + lira "furrow, earth thrown up between two furrows," from PIE *leis- (1) "track, furrow" (see learn).
delirium tremens (n.): 1813, medical Latin, literally "trembling delirium," introduced 1813 by British physician Thomas Sutton, for "that form of delirium which is rendered worse by bleeding, but improved by opium. By Rayer and subsequent writers it has been almost exclusively applied to delirium resulting from the abuse of alcohol" [Sydenham Society Lexicon of Medicine]. As synonyms, Farmer lists barrel-fever, gallon distemper, blue Johnnies, bottle ache, pink spiders, quart-mania snakes in the boots, triangles, uglies, etc.
deliver (v.): c. 1200, "save, rescue, set free, liberate," from Old French delivrer "to set free; remove; save, preserve; hand over (goods)," also used of childbirth, from Late Latin deliberare, from de- "away" (see de-) + Latin liberare "to free" (see liberal (adj.)).

Childbirth sense in English, "to bring (a woman) to childbirth," is from c. 1300. Sense of "hand over, give, give up, yield" is c. 1300. in English, which brings it in opposition to its root. Meaning "project, throw" is 1590s. Related: Delivered; delivering.
deliverable (adj.): 1755, from deliver + -able.
deliverance (n.): c. 1300, "action of setting free" in physical or spiritual senses, from Old French deliverance (12c.), from délivrer (see deliver). Formerly also with senses now restricted to delivery.
delivery (n.): early 15c., "action of handing over to another," from Anglo-French delivrée, noun use of fem. past participle of Old French délivrer (see deliver). Childbirth sense is attested from 1570s. Of speech, from 1580s. Of a blow, throw of a ball, etc., from 1702.
dell (n.1): Old English dell "dell, hollow, dale" (perhaps lost and then borrowed in Middle English from cognate Middle Dutch/Middle Low German delle), from Proto-Germanic *daljo (source also of German Delle "dent, depression," Gothic ib-dalja "slope of a mountain"); related to dale (q.v.).
dell (n.2): rogue's cant 16c.-17c. for "a young girl of the vagrant class," of uncertain origin.
A Dell is a yonge wenche, able for generation, and not yet knowen or broken by the vpright man. ... [W]hen they have beene lyen with all by the vpright man then they be Doxes, and no Dells. [Thomas Harman, "A Caveat or Warning for Common Cursitors," 1567]
Della Crusca: 1796, from Italian Accademia della Crusca, literally "Academy of the Chaff," "the name of an Academy established at Florence in 1582, mainly with the object of sifting and purifying the Italian language; whence its name, and its emblem, a sieve" [OED].
Della Robbia: 1787, from name of a family of 15c. Florentine painters and sculptors; used of wares made by Luca Della Robbia (1400-1482), or those like them.
delouse (v.): 1918, from de- + louse. First used in reference to World War I armies. Related: Deloused; delousing.
Delphi: oracle town on slopes of Mount Parnassus, from Greek delphis "dolphin" (see dolphin). Supposedly Apollo assumed this form to found the shrine.
Delphic (adj.): 1590s, from Latin Delphicus, from Greek Delphikos, from Delphi (see Delphi).
delt (n.): short for deltoid (q.v.).
delta (n.): c. 1200, Greek letter shaped like a triangle, equivalent to our "D," the name from Phoenician daleth "tent door." Herodotus used it of the mouth of the Nile, and it was so used in English from 1550s; applied to other river mouths from 1790.
deltoid (adj.): 1741, in deltoid muscle, so called for its shape, from Greek deltoeides "triangular," literally "shaped like the letter delta;" see delta + -oid.
delude (v.): c. 1400, from Latin deludere "to play false; to mock, deceive," from de- "down, to one's detriment" (see de-) + ludere "to play" (see ludicrous). Related: Deluded; deluding.
deluge (n.): late 14c., from Old French deluge (12c.), earlier deluve, from Latin diluvium "flood, inundation," from diluere "wash away," from dis- "away" (see dis-) + -luere, comb. form of lavere "to wash" (see lave).
deluge (v.): 1590s; see deluge (n.). Related: Deluged; deluging.
delusion (n.): "act of misleading someone," early 15c.; as a form of mental derangement, 1550s, from Latin delusionem (nominative delusio) "a deceiving," noun of action from past participle stem of deludere (see delude).

Technically, delusion is a belief that, though false, has been surrendered to and accepted by the whole mind as a truth; illusion is an impression that, though false, is entertained provisionally on the recommendation of the senses or the imagination, but awaits full acceptance and may not influence action. Delusions of grandeur, the exact phrase, is recorded from 1840, though the two words were in close association for some time before that.
delusional (adj.): 1871, from delusion + -al (1).
delusive (adj.): c. 1600; see delusion + -ive.
deluxe (adj.): 1819, from French de luxe, literally "of luxury," from Latin luxus "excess, abundance" (see luxury).
delve (v.): Old English delfan "to dig" (class III strong verb; past tense dealf, past participle dolfen), common West Germanic verb (cognates: Old Saxon delban, Dutch delven, Middle High German telben "to dig"), from PIE root *dhelbh- (source also of Lithuanian delba "crowbar," Russian dolbit', Czech dlabati, Polish dłubać "to chisel;" Russian dolotó, Czech dlato, Polish dłuto "chisel"). Weak inflections emerged 14c.-16c. Related: Delved; delving.
dem: representing pronunciation of them in Jamaican speech, from 1868. As a minced form of damn, attested from late 14c.
demagnetize (v.): 1839; see de- + magnetize. Related: Demagnetized; demagnetizing.
demagogic (adj.): 1831; see demagogue + -ic. Greek had demagogikos "fit for or like a demagogue."
demagogue (n.): 1640s, from Greek demagogos "popular leader," also "leader of the mob," from demos "people" (see demotic) + agogos "leader," from agein "to lead" (see act (n.)). Often a term of disparagement since the time of its first use, in Athens, 5c. B.C.E. Form perhaps influenced by French demagogue (mid-14c.).
Indeed, since the term demagogos explicitly denotes someone who leads or shepherds the demos, the eventual use of this word as the primary epithet for a political panderer represents a virtual reversal of its original meaning. The word demagogos in fact implies that the people need someone to lead them and that political power, at least in part, is exercised appropriately through this leadership. [Loren J. Samons II, "What's Wrong With Democracy," University of California Press, 2004]
demagogue (v.): by 1964, American English, from demagogue (n.). Related: Demagogued; demagoguing.
demagoguery (n.): 1855; see demagogue + -ery. Demagogy in the same sense is from 1650s, from Greek demagogia "leadership of the people."
demand (v.): late 14c., "ask, make inquiry," from Old French demander (12c.) "to request; to demand," from Latin demandare "entrust, charge with a commission" (in Vulgar Latin, "to ask, request, demand"), from de- "completely" (see de-) + mandare "to order" (see mandate). Meaning "to ask for as a right" is early 15c., from Anglo-French legal use. Related: Demanded; demanding.
demand (n.): late 13c., "a question," from Old French demande (see demand (v.)). Meaning "a request, claim" is from c. 1300. In the political economy sense (correlating to supply) it is attested from 1776 in Adam Smith.
demanding (adj.): early 15c., "asking, questioning," present participle adjective from demand (v.). Meaning "insistent" is by late 19c. Related: Demandingly.
demarcate (v.): 1816, back-formation from demarcation. Related: Demarcated; demarcating.
demarcation (n.): c. 1752, from Spanish linea de demarcacion or Portuguese linha de demarcaçao, name of the line laid down by Pope Alexander VI, May 4, 1493, dividing the New World between Spain and Portugal on a line 100 leagues west of the Cape Verde Islands. Applied from 1801 to other lines dividing regions. From Spanish de- (see de-) + marcar "to mark the boundaries of," from a Germanic source (see mark (n.1)).
demarche (n.): 1650s, "walk, step," from French démarche (15c.) literally "gait, walk, bearing," from démarcher (12c.) "to march," from de- (see de-) + marcher (see march (v.)). Meaning "a diplomatic step" attested from 1670s. A word never quite nativized.
demark (v.): 1650s, abstracted from demarcation and altered by influence of mark (v.).
dematerialize (v.): 1884; see de- + materialize. Related: Dematerialized; dematerializing.
demean (v.): "lower in dignity," c. 1600, perhaps from de- "down" + mean (adj.) and modeled on debase. Indistinguishable in some uses from obsolete demean (see demeanor) which influenced it and may be its true source. Related: Demeaned; demeaning.
demeaning (adj.): 1829, present participle adjective from demean (v.). Related: Demeaningly.
demeanor (n.): late 15c., from obsolete Middle English demean "handle, manage, conduct," later "behave in a certain way" (early 14c.), from Old French demener (11c.) "to guide, conduct; to live, dwell," from de- "completely" (see de-) + mener "to lead, direct," from Latin minare "to threaten," in Late Latin "to drive (a herd of animals);" see menace. Sense in English evolved from notion of "conduct, manage" (oneself). Spelling changed by influence of nouns in -or, -our.
demeanour: chiefly British English spelling of demeanor; for suffix, see -or.
dement (v.): "to drive mad," 1540s, probably from Middle French démenter, from Late Latin dementare "to drive out of one's mind," from stem of Latin demens "out of one's senses, insane, raving, foolish; distracting, wild, reckless" (a less technical term than insanitas), from phrase de mente, from de + mente, ablative of mens mind" (see mind (n.)).
demented (adj.): 1640s, from obsolete dement "drive mad."
dementia (n.): 1806, from Latin dementia "madness, insanity," literally "a being out of one's mind," from dement-, stem of demens "mad, raving" (see dement) + abstract noun suffix -ia. It existed earlier in an Englished form, demency (1520s), from French démence. Dementia praecox is a Modern Latin form recorded from 1899 in English, 1891 in German, from French démence précoce (1857). See precocious.
demerit (n.): late 14c., from Old French desmerite "blame, demerit" (Modern French démérite), from des- "not, opposite" (see dis-) + merite "merit" (see merit (n.)). Latin demereri meant "to merit, deserve," from de- in its completive sense. But Medieval Latin demeritum meant "fault." Both senses existed in the Middle French form of the word. Meaning "penalty point in school" is attested from 1862.
Demerol: trademark name, by 1942; originally a morphine substitute.
demesne (n.): c. 1300, demeyne (modern spelling by late 15c.), from Anglo-French demesne, demeine, Old French demaine "land held for a lord's own use," from Latin dominicus "belonging to a master," from dominus "lord." Re-spelled by Anglo-French legal scribes under influence of Old French mesnie "household" (and the concept of a demesne as "land attached to a mansion") and their fondness for inserting -s- before -n-. Essentially the same word as domain.
Demeter: goddess of agriculture, mother of Persephone, from Greek Demeter; the second element generally given as mater (see mother); the first element possibly from da, Doric form of Greek ge "earth" (see Gaia), but Liddell & Scott find this "improbable." The Latin masc. proper name Demetrius means "son of Demeter."