Meaning

noun a punch made of sweetened ale or wine heated with spices and roasted apples; especially at Christmas

verb celebrate noisily, often indulging in drinking; engage in uproarious festivities

verb propose a toast to

originFrom Middle English wassail, from Old Norse ves heill (“be healthy!”), from the imperative of vesa (“to be”) + heill (“healthy”). The earliest documented use of the term is from the first part of the 12th century CE, in Geoffroy of Monmouth's Historia Regum Britanniae (see page's citations).

Etymology from Wiktionary, CC BY-SA 3.0