Black days of the week
Very rarely, dramatically bad days in history have come to be called Black [day of the week]--such as September 24, 1929, the beginning of the Wall Street Crash, called 'Black Thursday'. Far from all of the worst days in history have been so dubbed. For instance, the day of the 2004 Indian Ocean earthquake and tsunami, December 26, 2004, is not called "Black Sunday" but it was far blacker than the 'Black Sunday' that fell on January 21st 2001 (see below). See disaster.
- Black Monday Easter, 1209. A group of 500 settlers recently arrived in Dublin from Bristol were massacred by warriors of the O'Tooles and O'Beirnes. 
- Black Tuesday May 13th 2003. France was “crippled” by a 24-hour strike that brought chaos to the French transport system today as trade unions mobilised a mass protest against planned state pension reforms. 
- Black Wednesday September 16th 1992. The government of the UK was forced to withdraw the pound from the European Exchange Rate Mechanism. One speculator, George Soros, made over US$1 billion profit. In 1997, the UK Treasury estimated the cost of Black Wednesday at £3.4 billion.
- Black Thursday October 24th 1929. Beginning of the Wall Street Crash of 1929
- Black Friday September 24th 1869. A financial panic in the U.S. caused by two speculators’ efforts to corner the gold market on the New York Gold Exchange (Fisk-Gould Scandal). (More recently, the term has been used to refer to the day after Thanksgiving in the U.S., the start of the unofficial Christmas-shopping season, when many retailers offer special bargains.)
- Black Saturday August 4th 1621. A dark, stormy Saturday in Scotland, seen by some as a judgment of Heaven against Acts then passed in the Scots Parliament tending to establish Episcopacy.
- Black Sunday, January 21st 2001. Satellite television provider DirecTV transmitted an electronic message from its orbiting satellites that destroyed thousands of hacked smart cards, which had been allowing pirates to gain free access to hundreds of channels of programming for four years.