meltdown (Noun) — Severe overheating of the core of a nuclear reactor resulting in the core melting and radiation escaping.
meltdown (Noun) — A disaster comparable to a nuclear meltdown. ex. "there is little likelihood of a meltdown comparable to the American banking collapse in March 1933"
meltdown (Noun) — A display of bad temper. ex. "he had a meltdown"
meltdown (Verb) — Reduce or cause to be reduced from a solid to a liquid state, usually by heating. ex. "melt down gold"