Source : Webster's Revised Unabridged Dictionary (1913)

Sib \Sib\, n. [AS. sibb alliance, gesib a relative. [root]289.
   See {Gossip}.]
   A blood relation. [Obs.] --Nash.

Sib \Sib\, a.
   Related by blood; akin. [Obs. or Prov. Eng. & Scot.] --Sir W.
   Scott.

         Your kindred is but . . . little sib to you. --Chaucer.

         [He] is no fairy birn, ne sib at all To elfs, but
         sprung of seed terrestrial.              --Spenser.

Source : WordNet®

sib
     n 1: a person's brother or sister [syn: {sibling}]
     2: one related by blood or origin; especially on sharing an
        ancestor with another [syn: {blood relation}, {blood
        relative}, {cognate}]