only child
US /ˈoʊn.li ˌtʃaɪld/
UK /ˈoʊn.li ˌtʃaɪld/

1.
외동, 외동아들, 외동딸
a child who has no siblings
:
•
Being an only child, she sometimes wished for a brother or sister.
외동딸이라서 가끔 오빠나 언니가 있었으면 좋겠다고 생각했다.
•
He grew up as an only child in a quiet neighborhood.
그는 조용한 동네에서 외동아들로 자랐다.