meltdown

noun9

1. •
   An act or process of melting.
2. •
   (Sudden) loss of control over one's behaviour, emotions, etc.; (countable) an instance of this.
3. •
   (informal, figurative) An emotional outburst; a fit, a tantrum.
4. •
   (figurative) A response to sensory overload or stress, in which an autistic person is overwhelmed by intense, seemingly disproportionate emotions, behaving erratically and becoming unable to mask (“act more neurotypically”).

   • If you're experiencing challenges that are extremely stressful and may lead you to being overwhelmed, or set off a meltdown in the workplace, this may be very concerning to your work colleagues. — 2022
5. •
   (informal, figurative) Synonym of nervous breakdown (“an attack of a psychological disorder such as anxiety or depression which is so severe that it prevents a person from continuing to function normally”); also (loosely), a situation where one is unable to function mentally due to panic, stress, etc.

   • After the huntsman raced across my windscreen, I had an arachnophobic meltdown on the side of the road. — 2025
6. •
   Severe uncontrolled overheating and melting of the fuel in the core of a nuclear reactor, with the potential for radiation to escape; (countable) an instance of this.
7. •
   (figurative) Chiefly preceded by a descriptive word: uncontrolled disorder which often has disastrous consequences; (countable) a situation involving this; a crisis.

   • Channel 4 switchboards went into meltdown this week when viewers called to complain about a Brass Eye programme on child sex. — 2001
8. •
   (figurative) Synonym of crash (“a sudden large decline in the value of money, stocks or other assets, etc., especially one that causes additional economic difficulties”).
9. •
   (rare) A mass of melted material.