a woman or girl in relation to other daughters and sons of her parents

I had nine brothers and sisters

a 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 female fellow adherent of a religion or member of a religious denomination

a senior female nurse, typically in charge of a ward

the ward sister needs to be consulted

Sister nodded, glancing at the reports