A tattler; a sponsor at baptism, a corruption of gossib, which is Godsib, a kinsman in the Lord. (Sib, gesib, Anglo-Saxon, kinsman, whence Sibman, he is our sib, still used.)
“Tis not a maid, for she hath had gossips [sponsors for her child]: yet `tis a maid, for she is her master's servant, and serves for wages.” —Shakespeare: Two Gentlemen of Verona, iii.1.
“Here, andrew, carry this to my gossip, jolly father Boniface, the
monk of St. Martin's” —
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894