The Collaborative International Dictionary of English v.0.48:

Sib \Sib\ (s[i^]b), n. [AS. sibb alliance, gesib a relative.
   [root]289. See Gossip.]
   1. A blood relation. [Obs.] --Nash.
      [1913 Webster]

   2. a sibling.
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Sib \Sib\, a.
   Related by blood; akin. [Obs. or Prov. Eng. & Scot.] --Sir W.
   Scott.
   [1913 Webster]

         Your kindred is but . . . little sib to you. --Chaucer.
   [1913 Webster]

         [He] is no fairy birn, ne sib at all
         To elfs, but sprung of seed terrestrial. --Spenser.
   [1913 Webster]

WordNet (r) 3.0 (2006):

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

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "sib":
   affiliated, agnate, akin, allied, ancestry, avuncular, blood,
   blood relation, blood relative, clansman, closely related, cognate,
   collateral, collateral relative, congeneric, connections,
   consanguine, consanguinean, consanguineous, distaff side,
   distant relation, distantly related, enate, family, flesh,
   flesh and blood, folks, foster, friendly, german, germane, kin,
   kindred, kinfolk, kinnery, kinsfolk, kinsman, kinsmen, kinswoman,
   kith and kin, matrilateral, matrilineal, matroclinous,
   near relation, next of kin, novercal, of the blood, patrilateral,
   patrilineal, patroclinous, people, posterity, receptive, related,
   relations, relatives, sibling, spear kin, spear side, spindle kin,
   spindle side, sword side, tribesman, uterine, uterine kin,
   well-disposed



V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

SIB
       Service Independent building Block (IN)