Definitions

1. adjective

given to or characterized by noisy, boisterous, or rowdy behavior, especially in a merry or festive manner

“The roisterous students were thrown out of the library for making too much noise.”

2. noun

a noisy, boisterous, or rowdy person or group, especially in a merry or festive manner

“The roisterous crowd at the music festival was a sight to behold.”