roister vs wassail

roister is not a noun while wassail is a noun.

Word	Noun	Adjective	Verb	Adverb
roister	No	No	Yes	No
wassail	Yes	No	Yes	No

As verbs, wassail is a hypernym of roister; that is, wassail is a word with a broader meaning than roister:

roister: engage in boisterous, drunken merrymaking
wassail: celebrate noisily, often indulging in drinking; engage in uproarious festivities

Other hypernyms of roister include jollify, make happy, make merry, make whoopee, racket, revel, whoop it up.

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

roister (verb)	wassail (verb)
engage in boisterous, drunken merrymaking	propose a toast to
	celebrate noisily, often indulging in drinking; engage in uproarious festivities