The Collaborative International Dictionary of English v.0.48:

Sister \Sis"ter\, n. [OE. sister, fr. Icel. systir; also suster,
   from AS. sweostor, sweoster, swuster, akin to OFries.
   sweester, suster, LG. s["u]ster, suster, D. zuster, OS. &
   OHG. swestar, G. schwester, Icel. systir, Sw. syster, Dan.
   s["o]ster, Goth. swistar, Lith. ses?, Russ. sestra, Pol.
   siostra, L. soror, Skr. svasr. [root]298. Cf. Cousin.]
   1. A female who has the same parents with another person, or
      who has one of them only. In the latter case, she is more
      definitely called a half sister. The correlative of
      brother.
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            I am the sister of one Claudio.       --Shak.
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   2. A woman who is closely allied to, or assocciated with,
      another person, as in the sdame faith, society, order, or
      community. --James ii. 15.
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   3. One of the same kind, or of the same condition; --
      generally used adjectively; as, sister fruits. --Pope.
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   Sister Block (Naut.), a tackle block having two sheaves,
      one above the other.

   Sister hooks, a pair of hooks fitted together, the shank of
      one forming a mousing for the other; -- called also match
      hook.

   Sister of charity, Sister of mercy. (R. C. Ch.) See under
      Charity, and Mercy.
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