IPA: //ˈbɔɪstərəsnəs//
KK: /ˈbɔɪstərəsnəs/
The quality of being noisy, energetic, and cheerful, often in a lively or rowdy way.
The boisterousness of the children playing in the park filled the air with laughter.
Boisterousness is formed from "boisterous" (originating from Middle English *boistous*, meaning rough or noisy) and the suffix "-ness" (meaning the state or quality of). The word describes the state of being rough, noisy, or exuberant.
Think of the word 'boisterous' which means noisy and lively, and remember that 'boisterousness' refers to the quality of being noisy and exuberant.