Online Etymology Dictionary

meh: expression of apathy or indifference, by 2003 (perhaps from 1992).
Meiji: "period of rule of emperor Mutsuhito" (1868-1912), which was marked by modernization and Westernization, 1873, from Japanese, literally "enlightened government."
mein (n.): "Chinese wheat flour noodles" (in lo mein, chow mein, etc.), 1934, from Chinese, literally "wheat flour."
meiosis (n.): "division of a cell nucleus," 1905, from Greek meiosis "a lessening," from meioun "to lessen," from meion "less," from PIE root *mei- "small" (see minus).

Earlier (1580s) it was a rhetorical term, a figure of speech "weak or negative expression used for a positive and forcible one, so that it may be made all the more emphatic," as when one says "not bad" meaning "very good" or "don't mind if I do" meaning "I really would like to," or this example from "Mark Twain":
"YOUNG AUTHOR." -- Yes Agassiz does recommend authors to eat fish, because the phosphorus in it makes brains. So far you are correct. But I cannot help you to a decision about the amount you need to eat,--at least, not with certainty. If the specimen composition you send is about your fair usual average, I should judge that perhaps a couple of whales would be all you would want for the present. Not the largest kind, but simply good, middling-sized whales.
Related: meiotic; meiotically.
meistersinger (n.): 1845, from German Meistersinger, literally "master singer;" see master (adj.) + singer.
Mekong: river in Southeast Asia, Thai, from me "mother" + khong "river, large stream."
melancholia (n.): 1690s, from Modern Latin melancholia (see melancholy).
melancholiac (n.): 1863, from melancholy. Earlier in same sense was melancholian (mid-14c.).
melancholic (adj.): late 14c., from melancholy + -ic, or else from Late Latin melancholicus, from Greek melankholikos "choleric," from melankholia “sadness” (see melancholy). As a noun, from 1580s. Earlier adjective formation was melancholian (mid-14c.), and melancholiac (mid-19c.) also was tried.
melancholy (n.): c.1300, "condition characterized by sullenness, gloom, irritability," from Old French melancolie "black bile, ill disposition, anger, annoyance" (13c.), from Late Latin melancholia, from Greek melankholia "sadness," literally (excess of) "black bile," from melas (genitive melanos) "black" (see melanin) + khole "bile" (see Chloe). Medieval physiology attributed depression to excess of "black bile," a secretion of the spleen and one of the body's four "humors."

The Latin word also is the source of Spanish melancolia, Italian melancolia, German Melancholie, Danish melankoli, etc. Old French variant malencolie (also in Middle English) is by false association with mal "sickness."
melancholy (adj.): late 14c., "with or caused by black bile; sullen, gloomy, sad," from melancholy (n.); sense of "deplorable" (of a fact or state of things) is from 1710.
Melanesia: one of three large divisions of Pacific islands, 1840, from a continental language, from melano- + nesos "island" (see Chersonese) + -ia. Modeled after Polynesia and meant to signify "the islands inhabited by blacks."
La Melanesia comprende la grande isola Australia, e quelle degli arcipelaghi di Salomone, di Lapèrouse, di Quiros, e dei gruppi della Nuova Caledonia, di Norfolk, e della Diemenin. A cagione dei Neri Oceanici, che, quasi esclusivamente, ne popolano le regioni, questa parte della Oceania ebbe dai moderni geografi e viaggiatori (il Graberg, il Rienzi, il d'Urville, ec.) il nome di Melanesia. ["Corso di Geografia Universale," Firenze, 1839]
Melanesian (adj.): 1840, from Melanesia + -ian.
melange (n.): 1650s, from French mélange (15c.), from mêler "to mix, mingle," from Old French mesler (see meddle).
melanin (n.): dark brown or black pigment found in animal bodies, 1832, Modern Latin, with chemical suffix -in (2); first element from Greek melas (genitive melanos) "black," from PIE root *mel- "dark, soiled, dirty" (cf. Sanskrit malinah "dirty, stained, black," Lithuanian melynas "blue," Latin mulleus "reddish"). Related: Melanism; melanistic.
melanism (n.): 1843, from melano- + -ism.
melano-: word-forming element meaning "black," from Greek melano-, comb. form of melas (genitive melanos) "black, dark, murky" (see melanin).
melanoma (n.): "tumor containing melanin," 1826, medical Latin, from Greek melas (genitive melanos) "black" (see melanin) + -oma.
melanosis (n.): 1823, medical Latin, from Greek melanosis "a becoming black," from melanoun "to become black," from melas (genitive melanos); see melanin. Related: Melanotic.
melatonin (n.): 1958, from Greek melas "black, dark" (see melanin) + ending from serotonin. So called because its secretion is inhibited by sunlight.
Melba: in various food preparations, especially peach Melba (1905) and Melba toast (1925) is in honor of Nellie Melba, stage name (based on Melbourne, Australia) of Australian-born operatic soprano Helen Mitchell (1861-1931).
Melbourne: city in Australia, named 1837 for William Lamb, 2nd Viscount Melbourne (1779-1848) then British Prime Minister; the title is from Melbourne Hall, Derbyshire. The place name is literally "mill stream," Old English Mileburne (1086).
Melchior: masc. proper name, literally "king of light," from Hebrew melekh "king" + or "light."
Melchizedek: name of a priest-king in the Old Testament, from Hebrew Malki-tzedeq, literally "king of righteousness," from melekh "king;" second element related to tzadaq "he was righteous," tzaddiq "just, righteous."
meld (v.): "to blend together, merge, unite" (intransitive), by 1910, of uncertain origin. OED suggests "perh. a blend of MELT v.1 and WELD v." Said elsewhere to be a verb use of melled "mingled, blended," past participle of dialectal mell "to mingle, mix, combine, blend."
[T]he biplane grew smaller and smaller, the stacatto clatter of the motor became once more a drone which imperceptibly became melded with the waning murmur of country sounds .... ["Aircraft" magazine, October 1910]
But it is perhaps an image from card-playing, where the verb meld is attested by 1907 in a sense of "combine two cards for a score:"
Upon winning a trick, and before drawing from the stock, the player can "meld" certain combinations of cards. [rules for two-hand pinochle in "Hoyle's Games," 1907]
The rise of the general sense of the word in English coincides with the craze for canasta, in which melding figures. The card-playing sense is said to be "apparently" from German melden "make known, announce," from Old High German meldon, from Proto-Germanic *meldojan (cf. Old English meldian "to declare, tell, display, proclaim"), and the notion is of "declaring" the combination of cards. Related: Melded; melding.
melee (n.): 1640s, from French mêlée, from Old French meslee "brawl, confused fight; mixture, blend" (12c.), noun use of fem. past participle of mesler "to mix, mingle" (see meddle). See also medley. Borrowed in Middle English as melle but lost and then reborrowed 17c.
meliorate (v.): 1550s, "to make better," back-formation from melioration or else from Late Latin melioratus, past participle of Latin meliorare "improve," from melior "better," used as comparative of bonus "good," but probably originally meaning "stronger," from PIE root *mel- "strong, great, numerous" (see multi-). Related: Meliorated; meliorating; melioration; meliorative.
melioration (n.): c.1400, "improvement," from Late Latin meliorationem (nominative melioratio), noun of action from past participle stem of Latin meliorare (see meliorate).
meliorism (n.): "belief that the world tends to become better," 1868, from Latin melior (see meliorate) + -ism. Related: Meliorist (1835).
melisma (n.): 1837, from Greek melisma "a song, an air, a tune, melody," from melos "music, song, melody; musical phrase or member," literally "limb," from PIE *mel- "a limb." Related: Melismatic.
Melissa: fem. proper name, from Latin, from Greek (Ionic) melissa (Attic melitta) "honeybee," also "one of the priestesses of Delphi," from PIE *melit-ya, suffixed form of *melit- "honey" (cf. Greek meli, Latin mel "honey; sweetness;" Albanian mjal' "honey;" Old Irish mil "honey," Irish milis "sweet;" Old English mildeaw "nectar," milisc "honeyed, sweet;" Old High German milsken "to sweeten;" Gothic miliþ "honey").
mell (v.): "to mix, meddle," c.1300, mellen, from Old French meller, variant of mesler (see meddle). Related: Melled; melling.
mellifluent (adj.): c.1600, from Middle French mellifluent and directly from Late Latin mellifluentem (nominative mellifluens), related to mellifluus (see mellifluous).
mellifluous (adj.): early 15c., "sweet, pleasing" (of an odor, a style of speaking or writing, etc.), from Late Latin mellifluus "flowing with (or as if with) honey," from Latin mel (genitive mellis) "honey" (related to Greek meli "honey;" see Melissa) + -fluus "flowing," from fluere "to flow" (see fluent). Related: Melifluously; melifluousness.
Mellotron (n.): type of electronic musical instrument, 1963, from mello(w) + (elec)tron(ic).
mellow (adj.): mid-15c., melwe "soft, sweet, juicy" (of ripe fruit), perhaps related to melowe, variant of mele "ground grain" (see meal (2)), influenced by Middle English merow "soft, tender," from Old English mearu. Meaning "slightly drunk" is from 1680s. Mellow yellow "banana peel smoked in an effort to get high" is from 1967. Related: Mellowly; mellowness.
mellow (v.): 1570s, from mellow (adj.). Related: Mellowed; mellowing.
melodeon (n.): 1847, variant of melodion, from German Melopdoin, from Melodie, from Old French melodie (see melody).
melodic (adj.): 1818, from French mélodique, from Late Latin melodicus, from Greek melodikos, from melodia (see melody).
melodious (adj.): late 14c., from Old French melodios "melodious; delightful" (French mélodieux), from Medieval Latin melodiosus, from Latin melodia (see melody). Related: Melodiously; melodiousness.
melodise (v.): see melodize; also see -ize. Related: Melodised; melodising.
melodize: 1660s, from melody + -ize. Related: Melodized; melodizing.
melodrama (n.): 1784 (1782 as melo drame), "a stage-play in which songs were interspersed and music accompanied the action," from French mélodrame (18c.), from Greek melos "song" (see melody) + French drame "drama" (see drama). Meaning "a romantic and sensational dramatic piece with a happy ending" is from 1883, because this was often the form of the original melodramas. Also from French are Spanish melodrama, Italian melodramma, German melodram. Related: Melodramatize.
melodramatic (adj.): 1776; from foreign source of melodrama on model of dramatic. Related: Melodramatically.
melody (n.): late 13c., from Old French melodie "music, song, tune" (12c.), from Late Latin melodia, from Greek meloidia "a singing, a chanting, choral song, a tune for lyric poetry," from melos "song, part of song" (see melisma) + oide "song, ode" (see ode).
melon (n.): late 14c., from Old French melon (13c.), from Medieval Latin melonem (nominative melo), from Latin melopeponem, a kind of pumpkin, from Greek melopepon "gourd-apple" (name for several kinds of gourds bearing sweet fruit), from melon "apple" (see malic) + pepon, a kind of gourd, probably noun use of pepon "ripe" (see pumpkin).

In Greek, melon was used in a generic way for all foreign fruits (cf. similar use of apple). The Greek plural of "melon" was used from ancient times for "a girl's breasts."
Melpomene: Muse of tragedy, from Latin, from Greek Melpomene, literally "songstress," from melpein "to sing," of unknown origin.
melt (v.): Old English meltan "become liquid, consume by fire, burn up" (class III strong verb; past tense mealt, past participle molten), from Proto-Germanic *meltanan; fused with Old English gemæltan (Anglian), gemyltan (West Saxon) "make liquid," from Proto-Germanic *gamaltijanan (cf. Old Norse melta "to digest"), both from PIE *meldh-, (cf. Sanskrit mrduh "soft, mild," Greek meldein "to melt, make liquid," Latin mollis "soft, mild"), from root *mel- "soft," with derivatives referring to soft or softened (especially ground) materials (see mild). Figurative use by c.1200. Related: Melted; melting.

Of food, to melt in (one's) mouth is from 1690s. Melting pot is from 1540s; figurative use from 1855; popularized with reference to America by play "The Melting Pot" by Israel Zangwill (1908).
melt (n.): 1854, "molten metal," from melt (v.). In reference to a type of sandwich topped by melted cheese, 1980, American English.
meltdown (n.): by 1937 in the ice-cream industry; by 1956 in reference to a nuclear reactor, from verbal phrase, from melt (v.) + down (adv.). Metaphoric extension since 1979.