na-adjective, noun
voracious; having a hearty appetite
Describes a person or animal that eats eagerly and in large quantities. Often used in positive or admiring contexts.
彼は食欲旺盛で、いつもおかわりをする。
He has a hearty appetite and always asks for seconds.
食欲旺盛な子供たちのために、たくさん料理を作った。
I cooked a lot for the voracious children.
Compound of 食欲 (appetite) and 旺盛 (vigorous, abundant). The exact historical derivation is straightforward; both components are standard Sino-Japanese words.