Sib comes from Old English sibb ('kinship, relationship; a relative'), from Proto-Germanic *sibjō ('blood relationship, kinship'), from Proto-Indo-European *swe- ('one's own'). The historical chain includes Old English sibb and Proto-Germanic *sibjō. Older glosses in the chain include "kinship, relationship; a relative", "blood relationship, kinship", and "one", which help explain the semantic range of the modern word. Morphologically, sib is best read as borrowing, yielding an English noun and adjective shaped by both form history and later usage. In current English it functions as a noun and adjective, with the sense "a sibling or blood relative; related by kinship". English derivatives include sibship; related forms include sibling and gossip. The result is an English noun and adjective whose etymology preserves the older forms while supporting the word's specialized modern meaning.