To engage in boisterous merrymaking; revel noisily.
To behave in a blustering manner; swagger.
[From obsolete roister, roisterer, probably from Old French rustre, ruffian, alteration of ruste, from Latin rūsticus, rustic; see rustic.] rois'ter·er n., rois'ter·ous adj., rois'ter·ous·ly adv.