English definition of “sister”
/ˈsɪstər/ noun [C]
RELATIVE › a girl or woman who has the same parents as you: an older/younger sister my big/little sister
RELIGION (also Sister) › a nun (= woman who lives in a female religious group) : Sister Bridget
NURSE (also Sister) › a female nurse in the UK who is responsible for a hospital ward (= an area of a hospital containing beds for ill people) : I asked Sister if he would be able to go home soon.
MEMBER › a woman who is a member of the same race, religious group, organization, etc