Etymology
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rainbow (n.)

"arc of prismatic colors formed by the refraction of light rays by drops of rain or vapor," Middle English rein-bowe, from Old English renboga; see rain (n.) + bow (n.). Common Germanic compound (Old Frisian reinboga, Old Norse regnbogi, Swedish regenbåge, Dutch regenboog, German Regenbogen). The American rainbow trout (1876) is so called for its resplendent colors. Old English also had scurboga "shower-bow."

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smelt (n.)

Old English smelt "sardine, small salmon-like sea fish," cognate with Dutch smelt "sand eel," Danish smelt (c. 1600). OED notes that it has a peculiar odor (but doesn't suggest a connection with smell); Klein suggests a connection with the way the fish melts in one's mouth. Century Dictionary speculates it means "smooth" and compares Old English smeolt, smylt "serene, smooth." Watkins says from PIE root *mel- (1) "soft."

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smelt (v.)

mid-15c. (implied in smelter), from Dutch or Low German smelten, from Proto-Germanic *smelt- (source also of Old High German smelzan, German schmelzen "to melt"), from PIE *smeld-, variant of PIE root *mel- (1) "soft." Thus the word is related to melt (v.). Related: Smelted; smelting.

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iridescent (adj.)

1784, literally "rainbow-colored," coined from Latin iris (genitive iridis) "rainbow" (see iris). The verb iridesce (1868) is a back-formation. Related: Iridescently.

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smelter (n.)

mid-15c., agent noun from smelt (v.).

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enamel (v.)

"to lay enamel upon, cover or decorate with enamel," early 14c., from Anglo-French enamailler (early 14c.), from en- "in" (see en- (1)) + amailler "to enamel," variant of Old French esmailler, from esmal "enamel," from Frankish *smalt, from Proto-Germanic *smaltjan "to smelt" (see smelt (v.)). Related: Enameled; enameler; enameling.

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iris (n.)

late 14c. as the name of a flowering plant (Iris germanica); early 15c. in reference to the eye membrane, from Latin iris (plural irides) "iris of the eye; iris plant; rainbow," from Greek iris (genitive iridos) "a rainbow;" also "iris plant" and "iris of the eye," a word of uncertain origin, traditionally derived from PIE root *wei- "to bend, turn, twist."

Iris was the name of the minister and messenger of the Olympian gods (especially of Hera), visibly represented by the rainbow (which was regarded as the descent of a celestial messenger). From the oldest parts of the Iliad the word is used of both the messenger and the rainbow.

The eye region was so called (early 15c. in English) for being the part that gives color to the eye; the Greek word was used of any brightly colored circle, "as that round the eyes of a peacock's tail" [Liddell & Scott]. Another sense in Middle English was "prismatic rock crystal." Related: Iridian; iridine.

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*mel- (1)

Proto-Indo-European root meaning "soft," with derivatives referring to soft or softened materials.

It forms all or part of: amblyopia; bland; blandish; blenny; emollient; enamel; malacia; malaxation; malt; melt; mild; Mildred; milt; moil; mollify; Mollusca; mollusk; mulch; mullein; mutton; schmaltz; smelt (v.); smelt (n.).

It is the hypothetical source of/evidence for its existence is provided by: Sanskrit mrdh "to neglect," also "to be moist;" Greek malakos "soft," malthon "weakling;" Latin mollire "soften," mollis "soft;" Old Irish meldach "tender."

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found (v.2)

"to cast metal," late 14c., originally "to mix, mingle," from Old French fondre "pour out, melt, smelt" (12c.), from Latin fundere (past participle fusus) "to melt, cast, pour out," from nasalized form of PIE root *gheu- "to pour." Meaning "to cast metal" is from 1560s. Related: Founded; founding.

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iridium (n.)

silver-white metallic element, 1804, coined in Modern Latin by its discoverer, English chemist Smithson Tennant (1761-1815) from Greek iris (genitive iridos) "rainbow" (see iris) + chemical ending -ium. So called "from the striking variety of colours which it gives while dissolving in marine acid" [Tennant]

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