thanksgiving

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

• noun An act of giving thanks; an expression of gratitude, especially to God.
• noun Thanksgiving Day.

from The Century Dictionary.

• noun The act of rendering thanks or of expressing gratitude for favors, benefits, or mercies; an acknowledgment of benefits received: used in the Old Testament for acknowledgment by the act of offering.
• noun A public celebration of divine goodness; specifically [capitalized], in the United States, Thanksgiving day (see the phrase below).
• noun A form of words expressive of thanks to God; a grace.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of rending thanks, or expressing gratitude for favors or mercies.
• noun A public acknowledgment or celebration of divine goodness; also, a day set apart for religious services, specially to acknowledge the goodness of God, either in any remarkable deliverance from calamities or danger, or in the ordinary dispensation of his bounties.

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

• noun an expression of gratitude.
• noun a short prayer said at meals; grace, a benediction.
• noun A public celebration in acknowledgement of divine favour.

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
• noun a short prayer of thanks before a meal