noun
adult; person of full age
Formal or legal term for a person who has reached the age of majority. In everyday speech, 大人 (おとな) is more common.
日本では、成年者は20歳以上と定義されていた。
In Japan, an adult was defined as a person aged 20 or older.
成年者としての権利と責任を理解する必要がある。
It is necessary to understand the rights and responsibilities as an adult.