1. A severe overheating of a nuclear reactor core, resulting in melting of the core and escape of radiation.
2. A disastrous situation; a failure or collapse: "No central bank or government institution existed ... to halt the meltdown, to stop the sudden run on the banks" (Evan I. Schwartz).
3. Informal An emotional breakdown.
The American Heritage® Dictionary of the English Language, Fifth Edition copyright ©2018 by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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