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English definition of “sister”

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sister

noun [C] uk   /ˈsɪs.tər/ us    /-tɚ/
A1 a girl or woman who has the same parents as another person: Sophie and Emily are sisters. Emily is Sophie's younger/little/older/big sister. a girl or woman who treats you in the kind way that a sister would: Lynn's such a good friend - she's like a sister to me. a woman who shares an interest with you, especially that of improving women's rights: [as form of address] "We must continue the fight, sisters!" US old-fashioned informal used to address a woman: [as form of address] OK, sister, move it! UK a female nurse who is in charge of a department of a hospital: The sister told us that visiting hours were over. [as form of address] Excuse me, Sister, could I have some water?
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a female member of a religious group, especially a nun: Sister Bernadette [as form of address] God bless you, Sister.
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sister

adjective [before noun] uk   /ˈsɪs.tər/ us    /-tɚ/
belonging to a pair or group of similar and related things, such as businesses, usually owned or operated by the same person or organization: our sister company in Australia the US battleship Missouri and her sister ship, the Wisconsin
(Definition of sister from the Cambridge Advanced Learners Dictionary & Thesaurus © Cambridge University Press)
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