How do you say sister and brother in Korea?

In Korean, "sister" is said as "언니" (eonni) when referring to an older sister and "여동생" (yeodongsaeng) for a younger sister. "Brother" is "형" (hyeong) when referring to an older brother and "남동생" (namdongsaeng) for a younger brother. These terms reflect the importance of age hierarchy in Korean culture.