wassail has 11 distinct synonyms spread across 2 of its 3 senses. Each sense below keeps its own list, because a synonym belongs to a meaning and not to a word: swapping one sense's substitute into another sense's sentence is how a thesaurus makes writing worse. WordNet records no antonym for it — antonymy is a relation between word forms rather than concepts, so it is deliberately sparse.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
celebrate noisily, often indulging in drinking; engage in uproarious festivities
“The members of the wedding party made merry all night”
a punch made of sweetened ale or wine heated with spices and roasted apples; especially at Christmas
Synonyms, antonyms and the broader and narrower relations for wassail come from Princeton University’s WordNet. Full sources and licences.