동생
dongsaeng · TOPIK 1
younger sibling
👶 동생 = 同生: same (동) + born (생) — born of the same parents, after you
From Sino-Korean 同生, literally same-birth: someone born to the same parents. In Korean it narrowed to mean the younger one. 생 is the same born/life syllable as in 생일 (birthday) and 학생 (student).