monokini (n.) Look up monokini at Dictionary.com
1964, from mono- + bikini, on mistaken notion that the bi- element was the Greek prefix meaning "two."
monolith (n.) Look up monolith at Dictionary.com
"column consisting of a single large block of stone," 1848, from French monolithe (16c.), from Latin monolithus (adj.) "consisting of a single stone," from Greek monolithos "made of one stone," from monos "single, alone" (see mono-) + lithos "stone." Transferred and figurative use is from 1934.
monolithic (adj.) Look up monolithic at Dictionary.com
1825, "formed of a single block," from monolith + -ic. Figurative use from 1920.
monologue (n.) Look up monologue at Dictionary.com
1660s, "long speech by one person," from French monologue, from Late Greek monologos "speaking alone," from Greek monos "single, alone" (see mono-) + logos "speech, word," from legein "to speak" (see lecture (n.)).
monomania (n.) Look up monomania at Dictionary.com
"insanity in regard to a single subect or class of subjects," 1820, probably on model of earlier French monomanie, from Modern Latin monomania, from Greek monos "single, alone" (see mono-) + mania (see mania).
monomaniac (n.) Look up monomaniac at Dictionary.com
1833; see monomania + maniac. Related: Monomaniacal.
monomer (n.) Look up monomer at Dictionary.com
1914, from mono- + Greek meros "part" (see merit (n.)). Related: Monomerous.
monometallic (adj.) Look up monometallic at Dictionary.com
1877 in currency sense, from mono- + metallic.
mononuclear (adj.) Look up mononuclear at Dictionary.com
1886; see mono- + nuclear.
mononucleosis (n.) Look up mononucleosis at Dictionary.com
1920, coined from mononuclear + Modern Latin -osis "abnormal condition."
monophonic (adj.) Look up monophonic at Dictionary.com
of recordings, broadcasts, etc., "not stereo, having only one output signal," 1958, coined to be an opposite of stereophonic; from mono- + -phonic, from Greek phone "sound, voice" (see fame (n.)).
Monophysite Look up Monophysite at Dictionary.com
1690s, from Church Latin Monophysita, from Greek monophysites, from monos "single, alone" (see mono-) + physis "nature" (see physics). Christian (regarded in the West as a heretic) who believes there is only one nature in the person of Jesus Christ. Now comprising Coptic, Armenian, Abyssinian and Jacobite churches.
monoplane (n.) Look up monoplane at Dictionary.com
1907, a hybrid coined from mono- + second element of aeroplane. In old planes the wings formed a single surface running across the fuselage.
monopolistic (adj.) Look up monopolistic at Dictionary.com
1858; see monopoly + -istic.
monopolize (v.) Look up monopolize at Dictionary.com
1610s; see monopoly + -ize. Figurative use from 1620s. Related: Monopolized; monopolizing; monopolization.
monopoly (n.) Look up monopoly at Dictionary.com
"exclusive control of a commodity or trade," 1530s, from Latin monopolium, from Greek monopolion "right of exclusive sale," from mono- + polein "to sell," from PIE root *pel- (5) "to sell" (cognates: Sanskrit panate "barters, purchases," Lithuanian pelnas "gain," Old Church Slavonic splenu, Russian polon "prey, booty," Old Norse falr, Dutch veil, German feil "for sale, venal").

Alternative form monopole (1540s, from the Old French form of the word) was common in 16c. The popular board game, invented by Charles Darrow, is from 1935. Monopoly money "unreal currency" is attested from 1972, in reference to the paper used in the game.
monopolylogue (n.) Look up monopolylogue at Dictionary.com
"entertainment in which one actor performs as many characters," 1824, from mono- + poly- + -logue.
monorail (n.) Look up monorail at Dictionary.com
1897, a hybrid coined from mono- + rail (n.1).
monosyllabic (adj.) Look up monosyllabic at Dictionary.com
1824, of languages; 1828, of words; 1870, of persons, from monosyllable + -ic. Earlier form was monosyllabical (1680s, of words). Related: Monosyllabically.
monosyllable (n.) Look up monosyllable at Dictionary.com
1530s, from Latin monosyllabus "of one syllable," from Greek monosyllabos, from monos "single, alone" (see mono-) + syllabe "syllable" (see syllable).
monotheism (n.) Look up monotheism at Dictionary.com
"belief that there is but one god," 1650s, from Greek mono-, comb. form of monos "single, alone" (see mono-) + theos "a god" (see theo-).
monotheist (n.) Look up monotheist at Dictionary.com
1670s, from monotheism + -ist.
monotheistic (adj.) Look up monotheistic at Dictionary.com
1846, from monotheist + -ic.
monotone (n.) Look up monotone at Dictionary.com
"unvarying tone in music or speaking," 1640s; see monotony. OED says use of the word as a noun "is peculiar to Eng." Related: Monotonic; monotonically.
monotonous (adj.) Look up monotonous at Dictionary.com
1750, of sound, from Greek monotonos "of one tone" (see monotony). Transferred and figurative use, "lacking in variety, uninteresting," is from 1783. Related: Monotonously.
monotony (n.) Look up monotony at Dictionary.com
1706, originally in transferred sense of "wearisome, tiresome," from French monotonie (1670s), from Greek monotonia "sameness of tone, monotony," from monotonos "monotonous, of one tone," from monos "single, alone" (see mono-) + tonos "tone" (see tenet). Literal sense of "sameness of tone or pitch" in English is from 1724.
monotype (n.) Look up monotype at Dictionary.com
1881 in biology; 1882 in printers' arts; 1893 as a brand name of typesetting machine; see mono- + type.
monoxide (n.) Look up monoxide at Dictionary.com
"oxide with one oxygen atom in each molecule," 1869, from mono- + oxide.
Monroe Doctrine Look up Monroe Doctrine at Dictionary.com
1848, in reference to principles of policy contained in the message of U.S. President James Monroe to Congress on Dec. 2, 1823.
mons (n.) Look up mons at Dictionary.com
from Latin mons (plural montes) "mountain" (see mount (n.)); used in English in various anatomical senses, especially mons Veneris "mountains of Love," fleshy eminence atop the vaginal opening, 1690s; often mons for short.
monseigneur (n.) Look up monseigneur at Dictionary.com
c.1600, from French monseigneur (12c.), title of honor equivalent to "my lord," from mon "my" (from Latin meum) + seigneur "lord," from Latin seniorem, accusative of senior "older" (see senior (adj.)). Plural messeigneurs.
monsieur (n.) Look up monsieur at Dictionary.com
1510s, from French monsieur, from mon sieur "my lord," from sieur "lord," shortened form of seigneur (see monseigneur) It was the historical title for the second son or next younger brother of the king of France.
monsignor (n.) Look up monsignor at Dictionary.com
title conferred on some prelates, 1640s, from Italian monsignore "my lord," formed on model of French monseigneur (see monseigneur) from equivalent elements in Italian.
monsoon (n.) Look up monsoon at Dictionary.com
1580s, "trade wind of the Indian Ocean," from Dutch monssoen, from Portuguese monçao, from Arabic mawsim "time of year, appropriate season" (for a voyage, pilgrimage, etc.), from wasama "he marked." When it blows from the southwest (April through October) it brings heavy rain, hence "heavy episode of rainfall during the rainy season" (1747).
monster (n.) Look up monster at Dictionary.com
early 14c., "malformed animal or human, creature afflicted with a birth defect," from Old French monstre, mostre "monster, monstrosity" (12c.), and directly from Latin monstrum "divine omen, portent, sign; abnormal shape; monster, monstrosity," figuratively "repulsive character, object of dread, awful deed, abomination," from root of monere "warn" (see monitor (n.)). Abnormal or prodigious animals were regarded as signs or omens of impending evil. Extended by late 14c. to imaginary animals composed of parts of creatures (centaur, griffin, etc.). Meaning "animal of vast size" is from 1520s; sense of "person of inhuman cruelty or wickedness" is from 1550s. As an adjective, "of extraordinary size," from 1837. In Old English, the monster Grendel was an aglæca, a word related to aglæc "calamity, terror, distress, oppression."
monstrosity (n.) Look up monstrosity at Dictionary.com
1550s, "abnormality of growth," from Late Latin monstrositas "strangeness," from Latin monstrosus, a collateral form of monstruosus (source of French monstruosité); see monster. Earlier form was monstruosity (c.1400). Sense of "quality of being monstrous" is first recorded 1650s. Meaning "a monster" is attested from 1640s.
monstrous (adj.) Look up monstrous at Dictionary.com
mid-15c., "unnatural, deviating from the natural order, hideous," from Middle French monstrueux, from Latin monstruosus "strange, unnatural, monstrous," from monstrum (see monster). Meaning "enormous" is from c.1500; that of "outrageously wrong" is from 1570s. Earlier form monstruous (late 14c., from Old French monstruous) was "very common in the 16th c." [OED].
montage (n.) Look up montage at Dictionary.com
1929, from French montage "a mounting," from Old French monter "to go up, mount" (see mount (v.)). Originally a term in cinematography.
montagnard (n.) Look up montagnard at Dictionary.com
"mountaineer, highlander," 1842, from French montagnard, from montagne (12c., see mountain).
Montana Look up Montana at Dictionary.com
U.S. state, from Latinized form of Spanish montaña "mountain," from Latin mont-, stem of mons (see mountain). Proposed 1864 by U.S. Rep. James H. Ashley of Ohio when it was created as a territory from Nebraska Territory, in reference to the Rocky Mountains, which however traverse only one end of it. Admitted as a state 1889. Related: Montanan.
Montanist (n.) Look up Montanist at Dictionary.com
mid-15c., millenarian and severely ascetic sect that believed in continual direct inspiration of the spirit and offered prominent church roles to women, from Montanus, Christian-inspired prophet in the wilds of Phrygia c.160 C.E. The heresy persisted into the 6c. and helped bring prophecy into disrepute in the established Church. Related: Montanism.
monte (n.) Look up monte at Dictionary.com
gambling card game, 1824, from Spanish monte "mountain," from Latin montem (nominative mons), see mount (n.). So called from the heap of cards left after dealing. A favorite in California during the gold rush years. The three-card form (first attested 1877) is of Mexican origin.
Monte Carlo Look up Monte Carlo at Dictionary.com
Italian, literally "Charles's Mountain," founded 1866 and named for Charles III of Monaco (1818-1889). The car rally there dates to 1911.
Monte Carlo fallacy Look up Monte Carlo fallacy at Dictionary.com
1957, named for resort in Monaco famous for its gambling casinos. The fallacy of thinking that the probability of a particular outcome rises with the successive number of opposite outcomes. Contrary to the Monte Carlo fallacy, if the roulette wheel stops on black 99 times in a row, the chances that the 100th spin will be red are still just under 50-50.
Montenegro Look up Montenegro at Dictionary.com
Adriatic coastal nation, from Venetian Italian (Tuscan monte nero), literally "black mountain," a loan-translation of the local Slavonic name, Crnagora. Related: Montenegrine.
Monterey Look up Monterey at Dictionary.com
city in California, U.S., formerly the Spanish Pacific capital, named for the bay, which was named 1603 for Spanish colonist and viceroy of New Spain Conde de Monterrey. The Monterrey in Mexico also is named for him.
Montessori Look up Montessori at Dictionary.com
1912, in reference to the system of education through free but guided play, devised 1907 by Italian educationist Maria Montessori (1870-1952).
Montezuma's revenge Look up Montezuma's revenge at Dictionary.com
"severe intestinal infection," such as often suffered by non-natives in Mexico, 1962, in reference to Montezuma II (1466-1520), Aztec ruler at the time of the Spanish conquest of Mexico.
month (n.) Look up month at Dictionary.com
Old English monað, from Proto-Germanic *menoth- (cognates: Old Saxon manoth, Old Frisian monath, Middle Dutch manet, Dutch maand, Old High German manod, German Monat, Old Norse manaðr, Gothic menoþs "month"), related to *menon- "moon" (see moon (n.); the month was calculated from lunar phases). Its cognates mean only "month" in the Romance languages, but in Germanic generally continue to do double duty. Phrase a month of Sundays "a very long time" is from 1832 (roughly 7 and a half months, but never used literally).
monthly (adv.) Look up monthly at Dictionary.com
1530s, from month + -ly (2). As an adjective from 1570s. Old English had monaþlic, but the modern words seem to be separate formations.