"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 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 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]
"heavenly body which revolves about the earth monthly," Middle English mone, from Old English mona, from Proto-Germanic *menon- (source also of Old Saxon and Old High German mano, Old Frisian mona, Old Norse mani, Danish maane, Dutch maan, German Mond, Gothic mena "moon"), from PIE *me(n)ses- "moon, month" (source also of Sanskrit masah "moon, month;" Avestan ma, Persian mah, Armenian mis "month;" Greek mene "moon," men "month;" Latin mensis "month;" Old Church Slavonic meseci, Lithuanian mėnesis "moon, month;" Old Irish mi, Welsh mis, Breton miz "month"), from root *me- (2) "to measure" in reference to the moon's phases as an ancient and universal measure of time.
A masculine noun in Old English. In Greek, Italic, Celtic, and Armenian the cognate words now mean only "month." Greek selēnē (Lesbian selanna) is from selas "light, brightness (of heavenly bodies)." Old Norse also had tungl "moon," ("replacing mani in prose" - Buck), evidently an older Germanic word for "heavenly body," cognate with Gothic tuggl, Old English tungol "heavenly body, constellation," of unknown origin or connection. Hence Old Norse tunglfylling "lunation," tunglœrr "lunatic" (adj.).
Extended 1665 to satellites of other planets. Typical of a place impossible to reach or a thing impossible to obtain, by 1590s. Meaning "a month, the period of the revolution of the moon about the earth" is from late 14c.
To shoot the moon "leave without paying rent" is British slang from c. 1823 (see shoot (v.)); the card-playing sense perhaps was influenced by gambler's shoot the works (1922) "go for broke" in shooting dice. The moon race and the U.S. space program of the 1960s inspired a number of coinages, including, from those skeptical of the benefits to be gained, moondoggle (based on boondoggle). The man in the moon "fancied semblance of a man seen in the disk of the full moon" is mentioned since early 14c.; he carries a bundle of thorn-twigs and is accompanied by a dog. Some Japanese, however, see a rice-cake-making rabbit in the moon. The old moon in the new moon's arms (1727) is the appearance of the moon in the first quarter, in which the whole orb is faintly visible by earthshine.
c. 1600, "to expose to moonlight;" later "idle about, wander or gaze moodily" (1836), "move listlessly" (1848), probably on the notion also found in moonstruck. The meaning "to flash the buttocks" is recorded by 1968, U.S. student slang, from moon (n.) "buttocks" (1756), "probably from the idea of pale circularity" [Ayto]. See moon (n.). Related: Mooned; mooning.
a nautical term for a blue flag having a white square in the center, hoisted at the fore royal masthead as a signal to report on board as the vessel is about to go to sea, attested by c. 1800, from blue (adj.1), but the significance of peter is uncertain and disputed. Two common guesses are that it is an abbreviation of repeater or that it stands for French partir.