訓 さかん ・ 音 オウ
Sino-Vietnamese: vượng
The sun 日 beside a king 王 (which gives the sound): a sun shining like a king means flourishing and full of vigor.
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子供は好奇心が旺盛だ。 (こどもはこうきしんがおうせいだ)
Children are full of curiosity.