A female person who has the same parents as you.

Countable noun. Plural: sisters. Common collocations: older sister, younger sister, big sister, sister-in-law (your spouse's sister or your sibling's wife). Informal: sis.

'Sister city' refers to two cities in different countries that have a special partnership. 'Sisterhood' describes the bond between women who support each other. In a hospital, a 'Sister' (with capital S) is a senior nurse in British English.