from the GNU version of the Collaborative International Dictionary of English
- Easter Monday, so called from the severity of that day in 1360, which was so unusual that many of Edward III.'s soldiers, then before Paris, died from the cold.
- The first Monday after the holidays; -- so called by English schoolboys.
Sorry, no etymologies found.
By January 21st, Black Monday was upon us, the Spanish stock market registered its worst fall since 1987 with a drop of 7.54 percent, the Bombay stock exchange slid 7.41 percent, as brokers were unable to pay stock exchanges the money which they owed on the shares they had bought.
So, there was Black Monday 20 years ago, and I would say it's a bleak Friday.