What is "sister block"

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.

   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 hook.

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

n. (context nautical English) A tackle block having two sheaves, one above the other.