melt down

(noun) severe overheating of the core of a nuclear reactor resulting in the core melting and radiation escaping. Synonyms: meltdown, nuclear meltdown.

(noun) a disaster comparable to a nuclear meltdown. Synonyms: meltdown. Example: "There is little likelihood of a meltdown comparable to the american banking collapse in march 1933."

(verb) reduce or cause to be reduced from a solid to a liquid state, usually by heating. Synonyms: melt, run, melt down. Examples: "Melt butter." "Melt down gold." "The wax melted in the sun."