How to say Adult in Japanese | 大人 | NihongoClassroom 大Big 人Person Explanation The Japanese adjective '大人 (おとな)' means 'adult' It refers to someone who is fully grown or mature, both physically and mentally This word is often used to describe behavior, responsibility, or appearance associated with adulthood For example: He is an adult「彼は大人です」 (かれはおとな