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
I am the sister of one Claudio. --Shak.
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.
3. One of the same kind, or of the same condition; --
generally used adjectively; as, sister fruits. --Pope.
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
Sister of charity, Sister of mercy. (R. C. Ch.) See under
Charity, and Mercy.