Black Friday, the Friday, Sept. 24, 1869, when the attempt of Jay Gould and James Fisk, Jr., to create a corner in the gold market by buying all the gold in the banks of New York city, amounting to $15,000,000, culminated. For several days the value of gold had risen steadily, and the speculators aimed to carry it from 144 to 200. Friday the whole city was in a ferment, the banks were rapidly selling, gold was a 162 and a half, and still rising. Men became insane, and everywhere the wildest excitement raged, for it seemed probably that business houses must be closed, from ignorance of the prices to be charged for their goods. But in the midst of the panic it was reported that Secretary Boutwell of the United States Treasury had thrown $4,000,000 on the market, and at once gold fell, the excitement ceased, leaving Gould and Fisk the winners of $11,000,000. The day noticed above is what is generally referred to as Black Friday in the United States, but the term was first used in England, being applied in the first instance to the Friday on which the news reached London, Dec. 6, 1745, that the young Pretender, Charles Edward, had arrived at Derby, creating a terrible panic; and finally to May 11, 1866, when the failure of Overend, Gurney & Co., London, the day before, was followed by a widespread financial ruin.

Entry from Everybody's Cyclopedia, 1912.