Thanksgiving Day

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The fourth Thursday of November, observed as a 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 expression of gratitude for harvest and health.
• noun The second Monday of October, celebrated in Canada by the expression of gratitude for harvest and health.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Canada A holiday, originally to give thanks to God for the harvest, celebrated annually on the second Monday of October.
• noun US A holiday, originally to give thanks to God and to commemorate the feast held by the Pilgrim colonists, celebrated annually on the fourth Thursday of November.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun fourth Thursday in November in the United States; second Monday in October in Canada; commemorates a feast held in 1621 by the Pilgrims and the Wampanoag