언니 · 오빠 · 형 · 누나

eon-ni · o-ppa · hyeong · nu-na · literally “Older sister / older brother (depends on your gender)”

Situation: Texting a friend who is two years older than you: 'Jiwon, are you free tomorrow?'

✕ What AI tells you

Outputs '지원아, 내일 시간 있어?' — the older friend's bare name plus casual speech, copying the English.

Why it fails: Calling someone older by their bare name (with 아/야) is how you address equals or juniors. Even close friends usually call an older friend with a kinship title, and AI also mixes up which title matches whose gender.

✓ What Koreans actually say

The title depends on BOTH your gender and theirs. Women say 언니 (older woman) and 오빠 (older man). Men say 누나 (older woman) and 형 (older man). Add the name for clarity: 지원 언니.

  • 언니, 내일 시간 있어요?

    eon-ni, nae-il si-gan i-sseo-yo

    A woman to an older female friend

  • 형, 내일 시간 있어?

    hyeong, nae-il si-gan i-sseo

    A man to an older male friend he's close with

  • 지원 선배님, 내일 시간 괜찮으세요?

    ji-won seon-bae-nim, nae-il si-gan gwaen-cha-neu-se-yo

    Older person from school or work you're not close to yet

Cultural nuance, in depth

Koreans establish relative age early in a relationship because it decides how people address each other. Kinship titles turn friends into a kind of chosen family and carry real warmth — 오빠 in particular can also sound affectionate or flirtatious, so context matters. Before you're close, 선배(님) or name + 씨 keeps a respectful distance. Moving to bare names usually happens only when the older person suggests it, often with 말 놓자 (let's drop the formal speech).