A nuclear “meltdown” (or “melt-down” or “melt down”) is a disaster that occurs when a nuclear reactor has melted its core. A “financial meltdown” or “(stock) market meltdown” is when the financial markets go down precipitously in a few days or even a few hours. The term “financial meltdown” has been cited in print since November 1981 and “market meltdown” since May 1986, but “meltdown” was popularly used to describe the stock market drop in October 1987.
 
The opposite term of “melt up” has been cited in print since at least May 1989.
 
 
The Free Dictionary
melt·down (mltdoun)
n.
1. Severe overheating of a nuclear reactor core, resulting in melting of the core and escape of radiation.
2. Informal A disastrous or rapidly developing situation likened to the melting of a nuclear reactor core: “After several corporate meltdowns, only two reporters remain in [the] bureau” (David Fitzpatrick).
3. Informal An emotional breakdown
 
Free Merriam-Webster Dictionary
melt·down noun \ˈmelt-ˌdau̇n\
Definition of MELTDOWN
1: the accidental melting of the core of a nuclear reactor
2: a rapid or disastrous decline or collapse
3: a breakdown of self-control (as from fatigue or overstimulation)
First Known Use of MELTDOWN
1956
 
(Oxford English Dictionary)
meltdown, n.
orig. U.S. fig. Any uncontrolled and usually disastrous event with far-reaching consequences; a sudden and decisive collapse; (Finance) a rapid drop in the value of a currency, assets, shares, etc.; a crash. Freq. with modifying word.
1983 S. Tolchin & M. Tolchin Dismantling Amer. vi. 189 (heading)  Political meltdown.
1986 Washington Post 2 June 3/1   They did this mostly, sources say, out of fear of the alternative—a mass fire sale of the EPIC properties. Such a ‘meltdown’, as it was referred to by lawyers on the case, could have had catastrophic repercussions in the nation’s mortgage markets.
1988 New Yorker 21 Mar. 25/1   Last October’s stock-market collapse‥was a ‘market meltdown’. A novelist wrote that his central character’s fraying nerves had brought about a ‘mental meltdown’.
1990 Vanity Fair (N.Y.) Aug. 160/1   If women are alienated, homosexuals have reached the meltdown stage.
1992 Financial Times 11 Apr. ii. 2/7   Talk of a meltdown in Japan plunging Wall Street into crisis and the US economy back into recession.
 
11 November 1981, Baltimore (MD) Sun, “Whoops” by John L. Hess, pg. A19:
Whoops is an expression of pleasurable excitement, except in the Pactific Northwest and on Wall Street. There it means a financial meltdown that makes Three Mile Island looks like a burnt marshmallow.
 
Whoops is the Washington Public Power Supply System (WPPS), a consortium of 25 small-city and rural utilities.
 
Google News Archive
23 October 1983, Ocala (FL) Star-Banner, “Big Buildup Over The Build-Down” by William Safire, pg. 5E, col. 1:
Word-coiners often find, to their dismay, some earlier use of their baby in a different context. Meltdown was an important new term in 1963, referring to the ultimate accident in a nuclear reactor and the fear that it could sizzle its way through the earth clear down to China. It is used metaphorically today throughout the language. In “Dismantling America: the Rush to Deregulate,” by Susan and Martin Tolchin, a chapter title is “Political Meltdown.” However, the first use of the word was in March 1937, in The Ice Cream Trade Journal: “Due to the clean meltdown…a cooler sensation results in the mouth than with gelatin ice cream.”
 
The alert reader is probably wondering: “If buildup led to build-down, why hasn’t meltdown led to melt-up?” Good question, alert reader, because in linguistics, just about everything that goes up has come down. However, the word formed by substituting a down for an up or vice versa is seldom opposite in meaning.
(...)
Melt-up is troublesome, however. An accident in a nuclear reactor in China?
 
OCLC WorldCat record
Washington Public Power Supply System : financial meltdown : oversight hearing before the Subcommittee on Mining, Forest Management, and Bonneville Power Administration of the Committee on Interior and Insular Affairs, House of Representatives, Ninety-eighth Congress, first session, on Washington Public Power Supply System, financial meltdown, hearing held in Portland, Oreg., June 10, 1983.
Author: United States. Congress. House. Committee on Interior and Insular Affairs. Subcommittee on Mining, Forest Management, and Bonneville Power Administration.
Publisher: Washington : U.S. G.P.O., 1983.
Edition/Format:  Book : National government publication : English
 
Google News Archive
1 May 1986, Beaver County Times (PA), “Dow Jones takes its worst beating” by James Russell (Knight Ridder Newspapers), pg. D1, col. 3:
The market meltdown was not a big surprise.
 
20 October 1987, Dallas (TX) Morning News, “Market ‘Meltdown’ Rocks Wall Sgtreet” by Doug J. Swanson:
NEW YORK—Searching for words to describe the worst one-day plunge in market history, the chairman of the New York Stock Exchange summoned images Monday of a nuclear power plant disaster.
 
“I call it the nearest thing to a melt-down I ever want to see,’ John J. Phelan Jr. said.
 
New York (NY) Times
MARKET TURMOIL; Real Estate Market Remains Rattled
By LISA BELKIN
Published: October 30, 1987
The stock market plunge is taking a toll on the real estate industry, many buyers, sellers and agents agree. But there is little agreement as to whether the disruption is temporary or likely to be long-lasting.
(...)
’‘There has been a weakening of activity and a weakening of prices,’’ said Lyle E. Gramley, chief economist of the Mortgage Bankers Association. ‘‘The remaining question is whether the stock market meltdown becomes an economic meltdown and a real estate meltdown.’’
   
New York (NY) Times
The Brady Report: Looking for Flaws; Study Cites Portfolio Insurers’ Role as a Key to the Market Meltdown
By ANISE C. WALLACE
Published: January 11, 1988
The report by a Presidential panel agreed with what some stock market participants have suspected for months: portfolio insurance managers were among the major villains in the frenetic five-day stock market drama of October 1987.
     
OCLC WorldCat record
Slowdown, meltdown, or rebound? : what’s ahead in politics, the economy, and finance? : financial conference April 20-23, 1988, Loews Ventana Canyon Resort, Tucson, Arizona
Author: Security Pacific Merchant Bank.
Publisher: [S.l.] : The Bank, 1988.
Edition/Format:  Book : Conference publication : English
 
30 May 1989, Winnipeg (Manitoba) Free Press, “Dreadful M-words exaggerate economic perils” by Jack McArthur, pg. 26, col. 1:
A minority of analysts is telling us of risks of melt-downs or melt-ups in markets.
 
You’ll recall the dreadful melt-down in the unprecedented, unreasoning crash of stock markets in a few days in 1987. Or in the globally vital U.S. dollar late in both ‘87 and ‘88.
 
A melt-up is the opposite, a wildly excessive rise caused by panic buying and leading almost inevitably to—what else?—a melt-down.
   
OCLC WorldCat
Financial meltdown as normal accident: the case of the American savings and loan industry
Author: S J Mezias
Edition/Format:  Article
Publication: ACCOUNTING ORGANISATIONS AND SOCIETY, 19, no. 2, (1994): 181
Database: British Library Serials
 
OCLC WorldCat record
Financial Meltdown Ahead?: Bracing for a Nuclear Bailout
Author: Sasha Abramsky
Publisher: New York, N.Y. : J.H. Richards,
Edition/Format:  Article : English
Publication: The nation. 261, no. 9, (1995): 312
Database: ArticleFirst
 
OCLC WorldCat record
13 bankers : the Wall Street takeover and the next financial meltdown
Author: Simon Johnson; James Kwak
Publisher: New York : Pantheon Books, ©2010.
Edition/Format:  Book : English : 1st edView all editions and formats
Summary: Johnson and Kwak examine not only how Wall Street’s ideology, wealth, and political power among policy makers in Washington led to the financial debacle of 2008, but also what the lessons learned portend for the future.