남동생
namdongsaeng · TOPIK 1
younger brother
👦 남 (男 male) + 동생 (younger sibling) = younger brother
남 is the hanja 男, male, and 동생 (同生, born of the same parents) means younger sibling. Swap 남 for 여 (女, female) and you get 여동생, younger sister. So the word is simply male + younger sibling.