Forefathers' Day

noun
  1. the anniversary of the day (December 21, 1620, in Old Style December 11) on which the Pilgrims landed at Plymouth, Mass. Owing to an error in changing the date from the Old Style to the New, it is generally observed on December 22.

Origin of Forefathers' Day

First recorded in 1820–30
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018