Definition from Wiktionary, the free dictionary
누나 • (nuna)
- elder sister of a male
- (by extension, spoken by a male) Unrelated female slightly older than oneself
- The term 누나 is often used by a male to address an elder female as a polite replacement for a second person singular pronoun (너 (neo) or 당신 (dangsin)).
- honorific: 누님 (nunim)