Etymology
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melt (v.)

Middle English melten, from Old English meltan (intransitive) "become liquid through heat" (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, reduce from a solid to a fluid state by means of heat" (transitive), from Proto-Germanic *gamaltijan (source also of Old Norse melta "to digest").

Both Germanic words are from PIE *meldh- (source also of Sanskrit mrduh "soft, mild," Greek meldein "to melt, make liquid," Latin mollis "soft, mild"), from root *mel- (1) "soft." Also in Middle English "dissolve" (of salt, sugar, etc.), "corrode" (of iron), "putrefy" (of flesh). Meaning "pass imperceptibly from one thing into another" is by 1781. Related: Melted; melting.

Figurative use "to diminish, wane; be touched, grow tender" is by c. 1200; transitive sense of "soften" (to love, pity, tenderness) is by early 14c. Of food, to melt in (one's) mouth is from 1690s. Melting point "degree of temperature at which a solid body melts" is by 1807. Melting pot is from early 15c.; figurative use from 1855; popularized with reference to immigrant assimilation in the United States by the play "The Melting Pot" by Israel Zangwill (1908):

DAVID Yes, East and West, and North and South, the palm and the pine, the pole and the equator, the crescent and the cross—how the great Alchemist melts and fuses them with his purging flame! Here shall they all unite to build the Republic of Man and the Kingdom of God. Ah, Vera, What is the glory of Rome and Jerusalem where all nations and races come to worship and look back, compared with the glory of America where all races and nations come to labour and look forward!
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melt (n.)

1854, "molten metal, a substance in a melted condition," from melt (v.). In reference to a type of sandwich (typically tuna) topped by melted cheese, by 1956, American English.

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molten (adj.)

"melted, in a state of solution," c. 1300, from archaic strong past participle of Old English meltian, a class III strong verb (see melt (v.)).

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melter (n.)

1530s, "one who melts," especially "the official who superintends the melting of gold and silver for coin in a mint," agent noun from melt (v.). By 1883 as "a furnace, pot, or crucible used for melting."

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meltdown (n.)

by 1922 as "an act or the process of melting metal;" by 1956 in reference to the accidental melting of the core of a nuclear reactor, from the verbal phrase (1630s), from melt (v.) + down (adv.). Metaphoric extension "breakdown in self-control" is attested since 1979.

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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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deliquesce (v.)

1756, in chemistry, "melt or dissolve gradually, become liquid by absorbing moisture from the air," from Latin deliquescere "to melt away," from de- (see de-) + liquescere "to melt," from liquere "to be liquid" (see liquid (adj.)). Transferred or figurative meaning "to melt away" is by 1858.

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deliquescent (adj.)

1791, in chemistry, "liquefying in air," from Latin deliquescentem (nominative deliquescens), present participle of deliquescere "to melt away," from de- (see de-) + liquescere "to melt," from liquere "to be liquid" (see liquid (adj.)). Transferred or figurative sense of "apt to dissolve or melt away" is by 1837. Related: Deliquescence.

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tabes (n.)
"emaciation," 1650s, medical Latin, from Latin tabes "a melting, wasting away, putrefaction," from tabere "to melt, waste away, be consumed," from PIE *ta- "to melt, dissolve" (see thaw (v.)).
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fondant (n.)
1877, from French fondant, noun use of present participle of fondre "to melt," from Latin fundere (past participle fusus) "to melt, cast, pour out," from nasalized form of PIE root *gheu- "to pour."
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