Lively; vigorous; full of energy or appetite — describing strong vitality, desire, or imagination.
祖母は年齢のわりに食欲が旺盛だ。
My grandmother has a good appetite for her age.
彼は好奇心旺盛で、何でも自分で試してみる。
He has a strong curiosity and tries everything himself.
旺盛な想像力がこの作品の魅力だ。
A rich imagination is what makes this work appealing.
Suffix meaning 'full of' — used to indicate something is brimming with energy, appetite, curiosity, etc.
学習意欲旺盛な学生が多い。
There are many students who are eager to learn.
繁殖力旺盛な種に注意が必要だ。
Care must be taken with species that breed prolifically.