Online Etymology Dictionary

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."
demi-: word-forming element meaning "half, half-sized, partial," early 15c., from Old French demi "half" (12c.), from Late Latin dimedius, from Latin dimidius "half, one-half," which contains the elements dis- "apart" (see dis-) + medius "middle" (see medial).
demi-monde (n.): 1855, also demimonde, from French demi-monde "so-so society," literally "half-world," from demi- "half" + monde, from Latin mundus "world" (see mundane).

Popularized by use as title of a comedy by Alexandre Dumas fils (1824-1895). Dumas' Demi-Monde "is the link between good and bad society ... the world of compromised women, a social limbo, the inmates of which ... are perpetually struggling to emerge into the paradise of honest and respectable ladies" ["Fraser's Magazine," 1855]. Not properly used of courtesans. Cf. 18th-century English demi-rep (1749, the second element short for reputation), defined as "a woman that intrigues with every man she likes, under the name and appearance of virtue ... in short, whom every body knows to be what no body calls her" [Fielding].
demigod (n.): 1520s, from demi- + god, rendering Latin semideus. The child of sexual intercourse between a deity and a mortal, a man raised to divine rank, or a minor god.
demijohn (n.): 1769, partial translation and word-play from French damejeanne (late 17c.) "Lady Jane," term used for large globular wicker-wrapped bottle, perhaps because its shape suggested a stout woman in the costume of the period. A general Mediterranean word, with forms found in Spanish, Portuguese, Italian, and Arabic.
demilitarize (v.): 1883, in reference to the Austrian military frontier in the Balkans; see de- + military + -ize. Demilitarized zone attested by 1921 (the Versailles Treaty uses neutralized zone).
demise (n.): mid-15c., from Middle French demise, fem. past participle of démettre "dismiss, put away," from des- "away" (from Latin dis-) + Middle French mettre "put," from Latin mittere "let go, send" (see mission). Originally "transfer of estate by will," meaning extended 1754 to "death" because that's when this happens.
demisemiquaver (n.): 1706; see demi- + semi- + quaver (n.).
demission (n.): 1570s, from French démission, from Latin demissionem "a sending away," noun of action from past participle stem of demittere (see demit).
demit (v.): 1610s (figurative), 1640s (literal), from Latin demittere "to send down," from de- + mittere "to send" (see mission).
demitasse (n.): also demi-tasse, 1842, from French, literally "half-cup," from demi- + tasse, an Old French borrowing from Arabic tassah, from Persian tasht "cup, saucer" (cf. Italian tazza, Spanish taza "cup").
demiurge (n.): 1670s, from Latinized form of Greek demiourgos, literally "public or skilled worker" (from demos "common people;" see demotic + ergos "work;" see urge (v.)).

The title of a magistrate in some Peloponnesian city-states and the Achæan League; taken in Platonic philosophy as a name for the maker of the world. In the Gnostic system, "conceived as a being subordinate to the Supreme Being, and sometimes as the author of evil" [OED].
demo (n.): short for demonstration (tape, disc, etc.). Music recording given out for promotional purposes, 1963. The word was used earlier to mean "a public political demonstration" (1936).
demob (v.): 1920, short for demobilize. Originally in reference to World War I troops returning to civilian life. Related: Demobbed.
demobilization (n.): 1866; see demobilize + -ation.
demobilize (v.): 1882; see de- (privative) + mobilize. Related: Demobilized; demobilizing.
democracy (n.): 1570s, from Middle French démocratie (14c.), from Medieval Latin democratia (13c.), from Greek demokratia "popular government," from demos "common people," originally "district" (see demotic), + kratos "rule, strength" (see -cracy).
Democracy implies that the man must take the responsibility for choosing his rulers and representatives, and for the maintenance of his own 'rights' against the possible and probable encroachments of the government which he has sanctioned to act for him in public matters. [Ezra Pound, "ABC of Economics," 1933]
democrat (n.): 1790, "adherent of democracy," with reference to France, from French démocrate (18c., opposed to aristocrate), back-formation from démocratie (see democracy); revived in U.S. as a political party affiliation 1798, with a capital D. As a shortening of this, Demo (1793) is older than Dem (c.1840).
democratic (adj.): c.1600, from French démocratique, from Medieval Latin democraticus, from Greek demokratikos "of or for democracy; favoring democracy," from demokratia (see democracy). Earlier was democratian (1570s).

As a political faction name, from 1790 in reference to France. U.S. political usage (with a capital D) attested from c.1800. The party originally was the Anti-Federal party, then the Democratic-Republican (Democratic for short). It formed among those opposed to extensive powers for the U.S. federal government. The name of the party was not formally shortened to Democratic until 1829. Democratic socialism is attested from 1849.
democratization (n.): 1865; see democratize + -ation.
democratize (v.): 1798 (transitive), 1840 (intransitive), from French démocratiser, from démocratie (see democracy). Greek demokratizein meant "to be on the democratic side."
demographic (adj.): 1891, from demography + -ic. As a noun, by 1998, short for demographic group or category. Related: Demographical; demographically.
demographics (n.): 1967, the science of divining from demographic statistics; see demography + -ics. Originally in reference to TV audiences and advertisers.
demography (n.): 1880, from Greek demos "people" (see demotic) + -graphy.
demoiselle (n.): 1510s, from French demoiselle (Old French dameiselle); see damsel.
demolish (v.): 1560s, from Middle French demoliss-, present participle stem of démolir "to destroy, tear down" (late 14c.), from Latin demoliri "tear down," from de- "down" (see de-) + moliri "build, construct," from moles (genitive molis) "massive structure" (see mole (n.3)). Related: Demolished; demolishing.
demolition (n.): 1540s, from Old French demolition (14c.) "demolition; defeat, rout," from Latin demolitionem (nominative demolitio), noun of action from past participle stem of demoliri (see demolish). Mencken noted demolition engineer for "house-wrecker" by 1936. Demolition derby is recorded from 1956, American English, defined by OED as "a contest in which old cars are battered into one another, the last one running being declared the winner."
demon (n.): c.1200, from Latin daemon "spirit," from Greek daimon "deity, divine power; lesser god; guiding spirit, tutelary deity" (sometimes including souls of the dead); "one's genius, lot, or fortune;" from PIE *dai-mon- "divider, provider" (of fortunes or destinies), from root *da- "to divide" (see tide).

Used (with daimonion) in Christian Greek translations and Vulgate for "god of the heathen" and "unclean spirit." Jewish authors earlier had employed the Greek word in this sense, using it to render shedim "lords, idols" in the Septuagint, and Matt. viii:31 has daimones, translated as deofol in Old English, feend or deuil in Middle English. Another Old English word for this was hellcniht, literally "hell-knight."

The original mythological sense is sometimes written daemon for purposes of distinction. The Demon of Socrates was a daimonion, a "divine principle or inward oracle." His accusers, and later the Church Fathers, however, represented this otherwise. The Demon Star (1895) is Algol.
demoness (n.): 1630s; see demon + -ess.
demonetization (n.): 1852, from French démonétisation, from démonetiser (see demonetize).
demonetize (v.): 1852, from French démonitiser, from de- (see de-) + monetiser (see monetize).
demoniac (adj.): c.1400, "possessed, insane," earlier (late 14c.) as a noun, "one who is possessed," from Late Latin daemoniacus (c.200), from Greek daimoniakos "possessed by a demon," from diamon (see demon).
demonic (adj.): 1660s, from Latin daemonicus, from daemon (see demon). Demonical is from late 15c.
demonize (v.): 1821, "to make into a demon" (literally or figuratively), from Medieval Latin daemonizare, from Latin daemon (see demon). Greek daimonizesthai meant "to be possessed by a demon." Related: Demonized; demonizing.
demonology (n.): 1590s; see demon + -ology.
demonstrable (adj.): c.1400, from Latin demonstrabilis, from demonstrare (see demonstration). Related: Demonstrably.
demonstrate (v.): 1550s, "to point out," from Latin demonstratus, past participle of demonstrare (see demonstration). Meaning "to point out by argument or deduction" is from 1570s. Related: Demonstrated; demonstrating.
demonstration (n.): late 14c., "proof that something is true," from Old French demonstration or directly from Latin demonstrationem (nominative demonstratio), noun of action from past participle stem of demonstrare "to point out, indicate, demonstrate," figuratively, "to prove, establish," from de- "entirely" (see de-) + monstrare "to point out, show," from monstrum "divine omen, wonder" (see monster). Meaning "public show of feeling," usually with a mass meeting and a procession, is from 1839. Related: Demonstrational.
demonstrative (adj.): late 14c., "characterized by logic, based on logic," from Old French démonstratif (14c.), from Latin demonstrativus "pointing out, demonstrating," from past participle stem of demonstrare (see demonstration). Grammatical sense, "pointing out the thing referred to," is mid-15c. Meaning "given to outward expressions of feelings" is from 1819. Demonstrative pronoun is late 16c.
demonstrator (n.): 1610s, "one who points out," agent noun in Latin form from demonstrate. From 1680s as "one who uses exhibits as a method of teaching;" 1870 as "one who participates in public demonstrations."
demoralize (v.): c.1793, "to corrupt the morals of," from French démoraliser, from de- "remove" (see de-) + moral (adj.) (see moral). Said to be a coinage of the French Revolution. Sense of "lower the morale of" (especially of armies) is first recorded 1848. Related: Demoralized; demoralizing.
demote (v.): 1881, American English coinage from de- + stem of promote. Said to have been Midwestern in origin.
Regarding an antithesis to 'promote,' the word universally in use in Cambridge, in Harvard College, is drop. The same word is in use in the leading schools here (Boston). I hope I may be counted every time against such barbarisms as 'demote' and 'retromote.' [Edward Everett Hale, 1892, letter to the publishers of "Funk & Wagnalls' Standard Dictionary"]
Related: Demoted; demoting.
demotic (adj.): 1822, from Greek demotikos "of or for the common people, in common use," from demos "common people," originally "district," from PIE *da-mo- "division," from root *da- "to divide" (see tide). In contrast to hieratic. Originally of the simpler of two forms of ancient Egyptian writing; broader sense is from 1831; used of Greek since 1927.
demotion (n.): 1901, agent noun from demote (v.).
demotivate (v.): 1976; see de- + motivate. Related: Demotivated; demotivating.
Dempsey: surname, from Irish Ó Diomasaigh "descendant of Diomasach," literally "proud."
demulcent (adj.): 1732, from Latin demulcentem (nominative demulcens), present participle of demulcere "to stroke down, soothingly pet," from de- (see de-) + mulcere "to soothe."
demur (v.): c.1200, "to linger, tarry, delay," from Old French demorer "delay, retard," from Latin demorari "to linger, loiter, tarry," from de- (see de-) + morari "to delay," from mora "a pause, delay" (see moratorium). Main modern sense of "raise objections" is first attested 1630s. Related: Demurred; demurring.