조신해요 · 조신했어요 · 조신한 (+noun)
well-mannered, demure, modest in behavior
Example
그 아이는 어른들 앞에서 늘 조신하게 행동해요.
That child always behaves politely in front of adults.
Word parts
조 control+신 body
Literally 'controlling one's body': careful in conduct and manners.