- 1[uncountable, countable] a serious accident in which the central part of a nuclear reactor melts, causing harmful radiation to escape
- 2[uncountable, countable] (economics) a situation where something fails or becomes weaker in a sudden or dramatic way The country is in economic meltdown. a meltdown on the New York Stock Exchange
- 3(informal) a loss of control over your emotions that happens very fast My little brother had a meltdown when he couldn’t get a new toy.
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