せいじん 成人 Common word JLPT N3 LinksSentence search for 成人Sentence search for せいじんKanji details for 成 and 人Edit in JMdict Noun1. adult; grownupそのえいが映画はせいじん成人しかみられない。Only adults may watch that film.Noun, Suru verb2. becoming an adult; coming of age; growing up (to be a man, woman)See also 新成人サンドラはせいじん成人してびじん美人になりました。Sandra has grown up to be a beautiful woman. Discussions Log in to talk about this word.