Etymology
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mold (n.1)

also mould, "hollow pattern of a particular form by which something is shaped or made," c. 1200, originally in a figurative sense, "fashion, form; nature, native constitution, character," metathesized from Old French modle "model, plan, copy; way, manner" (12c., Modern French moule), from Latin modulum (nominative modulus) "measure, model," diminutive of modus "manner" (from PIE root *med- "take appropriate measures").

By c. 1300 as "form into which molten metal, etc., is run to obtain a cast." By 1570s as "a form of metal or earthenware (later plastic) to give shape to jellies or other food. Figurative use of break the mold "render impossible the creation of another" is from 1560s.

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mold (n.2)

also mould, "minute, furry fungus," especially the types growing on neglected food and decaying organic matter, c. 1400, molde, probably from moulde, past participle of moulen "to grow moldy" (early 13c.), related to Old Norse mygla "grow moldy," possibly from Proto-Germanic *(s)muk- indicating "wetness, slipperiness," from PIE *meug- (see mucus). Or it might have evolved from (or been influenced by) Old English molde "loose earth" (see mold (n.3)).

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fungus (n.)
1520s, "a mushroom," from Latin fungus "a mushroom, fungus;" used in English at first as a learned alternative to mushroom (funge was used in this sense late 14c.). The Latin word is believed to be cognate with (or derived from) Greek sphongos, the Attic form of spongos "sponge" (see sponge (n.)). "Probably a loanword from a non-IE language, borrowed independently into Greek, Latin and Armenian in a form *sphong- ...." [de Vaan]
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blue (adj.2)
"lewd, indecent" recorded from 1840 (in form blueness, in an essay of Carlyle's); the sense connection with the color name (see blue (adj.1)) is unclear, and is opposite to that in blue laws (q.v.). John Mactaggart's "Scottish Gallovidian Encyclopedia" (1824), containing odd words he had learned while growing up in Galloway and elsewhere in Scotland, has an entry for Thread o'Blue, "any little smutty touch in song-singing, chatting, or piece of writing." Farmer ["Slang and Its Analogues Past and Present," 1890] offers the theory that this meaning derives from the blue dress uniforms issued to harlots in houses of correction (from c. 1600), but he writes that the earlier slang authority John Camden Hotten "suggests it as coming from the French Bibliothèque Bleu, a series of books of very questionable character," and adds, from Hotten, that, "Books or conversation of an entirely opposite nature are said to be Brown or Quakerish, i.e., serious, grave, decent."
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mold (v.)

also mould, mid-14c., "to mix, blend (something) by kneading;" late 14c. "to knead (bread), form into a particular shape," from mold (n.1). Figurative sense (of character, etc.) is from c. 1600. Related: Molded; molding.

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mold (n.3)

"fine, soft, loose earth," Old English molde "earth, sand, dust, soil; land, country, world," from Proto-Germanic *mulda (source also of Old Frisian molde "earth, soil," Old Norse mold "earth," Middle Dutch moude, Dutch moude, Old High German molta "dust, earth," Gothic mulda "dust"), from PIE root *mele- "to crush, grind." Specifically, since late (Christian) Old English, "the earth of the grave." Also, from c. 1300 as "earth as the substance out of which God made man; the 'dust' to which human flesh returns."

The proper spelling is mold, like gold (which is exactly parallel phonetically); but mould has long been in use, and is still commonly preferred in Great Britain. [Century Dictionary, 1897]
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blue (n.)

"the color of the clear sky," c. 1300, from blue (adj.1). From late 15c. as "blue clothing." The blue is from 1640s as "the sky" (hence bolt from the blue "lightning," 1837); from 1821 as "the sea." In reference to a particular party which has chosen blue for its color, by 1835. "In most parts of England the Conservative party" [OED], but in 17c. it often was the Whig color (opposed to royal red).

Blue was by c. 1600 the distinctive color of the dress of servants, which may be the reason police uniforms are blue, a tradition Farmer dates to Elizabethan times. Blue as the color of police uniforms in U.S. is by 1853, when New York City professionalized its force. They previously had had no regular uniforms, only badges.

An outburst of indignation followed [the order to wear uniforms]. The men declared the order was a violation of their rights as free men ; that no respecting American would wear livery, and raised a fund of five hundred dollars to test in the courts the authority of the Commissioners to compel them to wear uniforms. But the order was enforced when the day came. [John Bach McMaster, "A History of the People of the United States,"  vol. viii, 1913] 
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blue (v.)
"to make blue," c. 1600, from blue (adj.1).
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blue (adj.1)

"of the color of the clear sky," c. 1300, bleu, blwe, etc., "sky-colored," also "livid, lead-colored," from Old French blo, bleu "pale, pallid, wan, light-colored; blond; discolored; blue, blue-gray," from Frankish *blao or some other Germanic source, from Proto-Germanic *blæwaz (source also of Old English blaw, Old Saxon and Old High German blao, Danish blaa, Swedish blå, Old Frisian blau, Middle Dutch bla, Dutch blauw, German blau "blue").

This is from PIE *bhle-was "light-colored, blue, blond, yellow," from root *bhel- (1) "to shine, flash, burn," also "shining white" and forming words for bright colors. The same PIE root yielded Latin flavus "yellow," Old Spanish blavo "yellowish-gray," Greek phalos "white," Welsh blawr "gray," showing the slipperiness of definition in Indo-European color-words. Many Indo-European languages seem to have had a word to describe the color of the sea, encompassing blue and green and gray; such as Irish glass (from PIE root *ghel- (2) "to shine,"); Old English hæwen "blue, gray," related to har (see hoar); Serbo-Croatian sinji "gray-blue, sea-green;" Lithuanian šyvas, Russian sivyj "gray."

The present spelling in English is since 16c., common from c. 1700. The sense "lead-colored, blackish-blue, darkened as if by bruising" is perhaps by way of the Old Norse cognate bla "livid, lead-colored." It is the meaning in black and blue, and blue in the face "livid with effort" (1864, earlier black and blue in the face, 1829).

The color of constancy since Chaucer at least, but apparently for no deeper reason than the rhyme in true blue (c. 1500). Figurative meaning "sad, sorrowful, afflicted with low spirits" is from c. 1400, perhaps from the "livid" sense and implying a bruised heart or feelings. Of women, "learned, pedantic," by 1788 (see bluestocking). In some phrases, such as blue murder, it appears to be merely intensive.

Blue pencil as an editor's characteristic tool to mark corrections in copy is from 1885; also as a verb from 1885. The fabulous story of Blue-beard, who kept his murdered wives in a locked room, is from 1798. For blue ribbon see cordon bleu under cordon. Blue whale attested from 1851, so called for its color. Blue cheese is from 1862. Blue water "the open ocean" is from 1822. Blue streak, of something resembling a bolt of lightning (for quickness, intensity, etc.) is from 1830, Kentucky slang. Delaware has been the Blue Hen State at least since 1830, supposedly from a nickname of its regiments in the Revolutionary War.

The exact color to which the Gmc. term applies varies in the older dialects; M.H.G. bla is also 'yellow,' whereas the Scandinavian words may refer esp. to a deep, swarthy black, e.g. O.N. blamaðr, N.Icel. blamaður 'Negro' [Buck]
Few words enter more largely into the composition of slang, and colloquialisms bordering on slang, than does the word BLUE. Expressive alike of the utmost contempt, as of all that men hold dearest and love best, its manifold combinations, in ever varying shades of meaning, greet the philologist at every turn. [John S. Farmer, "Slang and Its Analogues Past and Present," 1890, p.252]
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blue-jeans (n.)
from 1843 as a type of fabric; see blue (adj.1) + jean. As short for blue-jeans trousers, from 1878.
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