sibling \sib"ling\ [sub + -ling.] (s[i^]b"l[i^]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]