I. ˈsib adjective
Etymology: Middle English, from Old English sibb, from sibb kinship; akin to Old High German sippa kinship, family, Latin sodalis comrade, Greek ēthos custom, character, Latin suus one's own — more at suicide
Date: before 12th century
: related by blood : akin
II. noun
Date: before 12th century
1.
a. : kindred , relatives
b. : a blood relation : kinsman
2. : a brother or sister considered irrespective of sex ; broadly : any plant or animal of a group sharing a degree of genetic relationship corresponding to that of human sibs
3. : a group of persons unilaterally descended from a real or supposed ancestor