1. An ancient expression of good wishes on a festive occasion, especially in drinking to some one. Geoffrey of Monmouth relates, on the authority of Walter Calenius, that this lady [Rowena], the daughter of Hengist, knelt down on the approach of the king, and, presenting him with a cup of wine, exclaimed, lord king waes heil, that is, literally, health be to you. (N. Drake)
2. An occasion on which such good wishes are expressed in drinking; a drinking bout; a carouse. In merry wassail he . . . Peals his loud song. The king doth wake to-night and takes his rouse, keeps wassail. (Shak) The victors abandoned themselves to feasting and wassail. (Prescott)
3. The liquor used for a wassail; especially, a beverage formerly much used in England at christmas and other festivals, made of ale (or wine) flavored with spices, sugar, toast, roasted apples, etc.; called also lamb's wool. A jolly wassail bowl, A wassail of good ale. (old Song)
Origin: AS. Wes hal (or an equivalent form in another dialect) be in health, which was the form of drinking a health. The form wes is imperative. See Was, and Whole.