The most common Korean word for “younger brother” is 남동생 (namdongsaeng). 「younger brother」는 한국어로 남동생.
Learn 남동생 free — flashcards, audio and review →「남동생」 단어장으로 무료로 외우기Words and levels: TOPIK I essentials (National Institute of Korean Language standard curriculum, KOGL Type 1) · examples: Cheesepotato