meltdown.

An act or process of melting.

An act or process of melting. 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.

A mass of melted material.

Chiefly preceded by a descriptive word: uncontrolled disorder which often has disastrous consequences; (countable) a situation involving this; a crisis.

Chiefly preceded by a descriptive word: uncontrolled disorder which often has disastrous consequences; (countable) a situation involving this; a crisis. Synonym of crash (“a sudden large decline in the value of money, stocks or other assets, etc., especially one that causes additional economic difficulties”).

(Sudden) loss of control over one's behaviour, emotions, etc.; (countable) an instance of this. An emotional outburst; a fit, a tantrum.

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

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