🙇 Address & Relationships
친구
"Friend" — but with a catch: in traditional Korean usage, chingu implies someone the same age as you, because equal age is what allows fully casual speech. Friends who are older or younger get relationship terms instead (hyung, unnie, noona, oppa, dongsaeng). You'll also see it in namja chingu (boyfriend) and yeoja chingu (girlfriend).
Literally: From the Sino-Korean 親舊, roughly "close" + "longtime."
우리 동갑이네! 그럼 친구 하자.
Uri donggabine! Geureom chingu haja.
→ We're the same age! Then let's be chingus.
K-drama fans see characters ask each other's age within minutes of meeting precisely to settle whether they can be chingu and drop into casual speech. The caveat: declaring yourself someone's chingu — and speaking casually — when they're older than you can genuinely offend; age-mates only, unless the older person explicitly invites it.
Oppa 오빠
The word a woman or girl uses for her older brother — and, by extension, for any older male she feels close to, including older male friends and boyfriends. Only female speakers use it; a man addressing an older man says "hyung" instead. Because it signals warmth and closeness, calling a non-relative "oppa" carries a flirtatious or affectionate undertone.
Unnie 언니
What a woman or girl calls her older sister, or an older female friend she's close to. It's strictly for female speakers; a man addressing an older woman says "noona" instead. It conveys affection and a sister-like bond rather than formality.
Hyung 형
What a man or boy calls his older brother, or an older male friend he's close to. It's for male speakers only; women use "oppa" for older males. Adding -nim ("hyungnim") makes it more deferential — or, in crime dramas, is how gang members address the boss.
Noona 누나
What a man or boy calls his older sister, or an older female friend he's close to. It's for male speakers only; women say "unnie" for older women. Like "oppa," it can carry romantic potential when used toward a non-relative.
Sunbae 선배
A senior at your school, workplace, or industry — someone who entered before you, regardless of their actual age. Both men and women use it, usually with the honorific suffix as "sunbaenim." The junior counterpart is "hoobae."
Hoobae 후배
A junior at your school, workplace, or industry — someone who entered after you, regardless of age. It's mostly used to describe the relationship rather than to address someone: you'd say "she's my hoobae," but call the person by their name. The senior counterpart is "sunbae."
Usage and nuance shift over time and between communities — treat this as a field guide, not a law book.