お姉(ねえ)さん

お姉(ねえ)さん is the polite term for 'older sister,' also used to address young women.

SENSE 1 - OLDER SISTER:
Used to refer to someone else's older sister, or when speaking to/about your own sister politely.

SENSE 2 - YOUNG WOMAN:
Used to address a young woman you don't know (like 'miss').

FAMILY TERM SYSTEM:

• 姉(あね): my older sister (humble, when talking to others)
• お姉(ねえ)さん: older sister (polite, for others' sisters)
• お姉(ねえ)ちゃん: older sister (casual/affectionate)
• 姉貴(あねき): older sister (masculine/rough speech)

CONTRAST WITH YOUNGER SISTER:

• 妹(いもうと): my younger sister
• 妹(いもうと)さん: younger sister (polite)

NOTE:
Children often call their own older sister お姉(ねえ)ちゃん or お姉(ねえ)さん directly.