1a woman or girl in relation to other daughters and sons of her parents:I had nine brothers and sisters
2a female friend or associate, especially a female fellow member of a trade union or other organization:textile unions are showing solidarity with their brothers and sisters in the developing world
a fellow woman seen in relation to feminist issues:uncloseted lesbian sisters
informal, chiefly North American a fellow black woman:‘Come on, sister, why not come clean and tell us?’
3 (often Sister) a member of a religious order of women:the sisters announced that there would be a special rosary every morning [as name]:Sister Elizabeth, the headmistress of the Convent High School
4 (often Sister)British a senior female nurse, typically in charge of a ward:the ward sister needs to be consulted [as name]:Sister nodded, glancing at the reports
5 [as modifier] denoting an organization or place which bears a relationship to another of common origin or allegiance or mutual association:Securicor and its sister company Securicor Servicesa sister ship
