sis‧ter S1 W1 [countable]
a girl or woman who has the same parents as you [↪ brother, half-sister, step-sister]:
Janet and Abby are sisters.
He has two sisters and a brother.
My older sister is a nurse.
Where's your little sister?
She's my twin sister.
a newspaper etc that belongs to the same group or organization:
the Daily Post's sister paper, the Liverpool Echo
3 also SisterRRC
Good morning, Sister Mary.
4 British English also SisterMN
a nurse in charge of a hospital ward:
the ward sister
I'm feeling a bit better today, Sister.
a word used by women to talk about other women and to show that they have feelings of friendship and support towards them:
We appeal to our sisters all over the world to stand by us.
6 American English spoken
a way of talking to or about an African-American woman, used especially by African Americans