sibling \sib"ling\ sub + -ling. si^b"li^ng, n.
   a brother or a sister.

   note: siblings have at least one parent in common. those
         related only by a common mother are uterine siblings;
         those related only by a common father are agnate
         siblings or consanguine siblings a legal term. a
         sibling having both parents in common is a
         sibling-german or a full brother or full sister.
         these modifying terms are more commonly used for the
         more specific uterine brother, uterine sister,
         agnate brother, brother-german, etc.
         pjc
see also:
uterine siblings agnate siblings consanguine siblings sibling-german full brother full sister 
uterine brother uterine sister agnate brother brother-german