Webster's Revised Unabridged Dictionary · 1913

Sib

Sib (sib) , noun

[Anglo-Saxon sibb alliance, gesib a relative. r289. See Gossip.]

1.
A blood relation. [Obsolete] — Nash
2.
a sibling.

Sib , adjective

Related by blood; akin. [Obsolete or Provincial English & Scottish] — Sir W. Scott
Your kindred is but... little sib to you. — Chaucer
[He] is no fairy birn, ne sib at all To elfs, but sprung of seed terrestrial. — Spenser