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.
Indo-European & Semitic Roots Appendices
Thousands of entries in the dictionary include etymologies that trace their origins back to reconstructed proto-languages. You can obtain more information about these forms in our online appendices:
The Indo-European appendix covers nearly half of the Indo-European roots that have left their mark on English words. A more complete treatment of Indo-European roots and the English words derived from them is available in our Dictionary of Indo-European Roots.