Definition of sib:
, by birth or descent; similar to
"1980: But she got up to go, and Domenico obeyed me too in mock meekness, making himself sib and coeval to Hortense, submissive to frowning elder brother, something incestuous in it. -- Anthony Burgess, Earthly Powers"
, relatives; kinsman
, blood relation; sibling
, brother or sister (irrespective of gender); in biology extended to any group of animals or plants sharing a corresponding genetic relation