Sis·ter n.
 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.
 3. One of the same kind, or of the same condition; -- generally used adjectively; as, sister fruits.
 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.