The roots of “roister” might lead us to think of a casual backyard bash. It can be traced back to the Latin “rusticus,” meaning “rustic.” If the mood of the party is cheerful but still rowdy, then you’re roistering. The adjective describes a specific sort of cheerful, boisterous celebration. However, not every loud gathering is roisterous (the adjective form of “roister”). A loud, heated protest could be described as clamorous, but not roisterous.