The short prayer traditionally said before Thanksgiving dinner is called grace.
Saying grace is a Christian mealtime custom involving a brief prayer or expression of thanks before—or sometimes after—eating. The word “grace” refers both to the prayer itself and to the act of offering thanks for the meal. Thanksgiving’s emphasis on gratitude makes the practice especially fitting, although not every household includes a prayer.
The custom has biblical roots: the New Testament describes Jesus and Saint Paul giving thanks before meals. Over time, different Christian denominations developed their own formulas, from a spoken blessing to a longer communal prayer. Some families use an improvised expression of gratitude instead.
“Benediction” is a common mix-up. It means a blessing, often given at the end of a religious service, while “matins” and “vespers” are traditional Christian services associated with morning and evening. A Thanksgiving prayer before eating can be a benediction in a broad sense, but the standard quiz answer for “saying ___” is grace.