na-adjective, noun
grand; lavish; large-scale; lively or thriving
Most often used for ceremonies, parties, celebrations, send-offs, and similar events, emphasizing impressive scale, splendor, and liveliness. The older or broader nuance of something being flourishing or thriving is tied to this idea of being vigorous and large in scale.
町は祭りを盛大に祝った。
The town celebrated the festival on a grand scale.
結婚式はとても盛大だった。
The wedding was very lavish.
式典は盛大を極めた。
The ceremony was magnificent in the extreme.
na-adjective, noun
powerful; vigorous; enthusiastic
Describes force or intensity rather than luxury; common with applause, cheers, welcomes, and other energetic public reactions.
演説が終わると、盛大な拍手が起こった。
When the speech ended, thunderous applause broke out.
観客は選手たちに盛大な声援を送った。
The crowd gave the players loud, enthusiastic cheers.