/ ˈsɪstə(r); NAmE / noun
1.
a girl or woman who has the same mother and father as another person :
She's my sister.
an older / younger sister
( informal )
a big / little / kid sister
We're sisters.
Do you have any brothers or sisters ?
My best friend has been like a sister to me (= very close) .
—see also half-sister , stepsister
2.
used for talking to or about other members of a women's organization or other women who have the same ideas, purpose, etc. as yourself :
They supported their sisters in the dispute.
3.
Sister ( BrE ) a senior female nurse who is in charge of a hospital ward
—see also charge nurse
4.
Sister a female member of a religious group, especially a nun :
Sister Mary
the Sisters of Charity
5.
(in the US) a member of a sorority (= a club for a group of female students at a college or university)
6.
( NAmE , informal ) used by black people as a form of address for a black woman
7.
(usually used as an adjective) a thing that belongs to the same type or group as sth else :
our sister company in Italy
a sister ship
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WORD ORIGIN
Old English , of Germanic origin; related to Dutch zuster and German Schwester , from an Indo-European root shared by Latin soror .