meltdown

noun

1. (countable)An act or process of melting.
2. (uncountable)An act or process of melting.

   “Thus began by far the gravest crisis in the troubled, 32-year history of commercial atomic power. A catastrophe had occurred over the weekend at the Chernobyl plant, 80 miles north of Kiev, where a reactor meltdown and explosion caused untold death and suffering and raised the prospect of long-term health and environmental damage on a far greater scale than anything yet unleashed by peaceful nuclear use.”

3. (countable, rare)A mass of melted material.
4. (figuratively, uncountable)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.”

   “Computer engineers were at a loss last night to explain why the Government had been hit by arguably the worst electronic meltdown in the history of Whitehall.”

   “If you're like me, you've looked at a paper coffee cup or an empty tube of toothpaste and thought, "Is this recyclable?" before tossing it in the recycling bin, hoping someone, somewhere, would sort it out. People in the waste management industry call this habit "wishcycling." […] [W]ishcycling is playing a big role in the current global recycling meltdown. […] Our uncertainty leads to climbing costs and waning productivity at recycling facilities; […]”

5. (countable, figuratively)Chiefly preceded by a descriptive word: uncontrolled disorder which often has disastrous consequences; (countable) a situation involving this; a crisis.
6. (countable, figuratively, informal)(Sudden) loss of control over one's behaviour, emotions, etc.; (countable) an instance of this.
7. (countable, figuratively, informal)(Sudden) loss of control over one's behaviour, emotions, etc.; (countable) an instance of this.

   “I was diagnosed with Asperger's syndrome in my forties. […] Now if I am really anxious, I can take a moment to think about what is making me anxious and what to do about it; before I would just spiral into a meltdown really quickly, with no understanding of why.”

   “As the brain starts becoming overwhelmed with stress chemicals, it has two primary ways of responding. […] [I]f the accumulation of stress chemicals, stimulation and/or demands are occurring too fast or are too intense to block out, then a meltdown is probable.”

   “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.”

8. (countable, figuratively, informal)(Sudden) loss of control over one's behaviour, emotions, etc.; (countable) an instance of this.

   “I had a major meltdown at work today. After being instructed one more time about additional work that I was to delegate to my direct reports, I snapped, but in a very polite manner. I excused myself from the boss' office and broke down completely in my cubicle.”

   “After the huntsman raced across my windscreen, I had an arachnophobic meltdown on the side of the road.”