Thanksgiving Day n. 1. The Fourth Thursday of November, observed as legal holiday in the United States to commemorate the feast held at Plymouth in 1621 by the Pilgrim colonists and members of the Wampanoag people and marked by the giving of thanks to God for harvest and health. 2. The second Monday of October, celebrated in Canada by the giving of thanks to God for harvest and health.
The American Heritage Dictionary , fourth edition
Happy Thanksgiving 2017