a day, October 12, observed as a holiday in various states of the U.S. in honor of the discovery of the New World by Columbus and his landing in the West Indies on October 12, 1492: observed in some states as the second Monday in October.
Origin of Columbus Day
An Americanism dating back to 1890–95
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British Dictionary definitions for columbus day
Oct 12, a legal holiday in most states of the US: the date of Columbus' landing in the West Indies (Caribbean) in 1492
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012