In Norse mythology, Sif is a golden-haired goddess associated with fertility and harvest. She is attested in the Poetic Edda, compiled in the 13th century from older traditional sources, the Edda of Snorri and the poetry of Scalde. In both "Edda" she is known for her golden hair and is married to Thor.
Snorri's Edda tells of Sif once having her hair shorn by Loki and Thor forcing Loki to have a golden helmet made for Sif, which not only gave Sif's golden hair but also five other items for other gods. Sif is also named as the mother of Þrúðr by Thor and Ullr.
Sif is one of the Aesir, and the wife of Thor. With him, she had Thrud. She is also the mother of Ullr, by an unspecified father. She is assimilated to the prophetess Sibyl and could transform herself into a swan.
She was present at the feast that Ægir offered to the Aesir.
The gold is called "Sif's hair", because Loki had cut off her hair, and replaced it with a hair made of gold, under the constraint of Thor, forged by the dwarves Brokk and Eitri. This hair had the power to grow like real hair and made her a symbol of beauty.
For Snorri Sturluson, Sif is identical to the giantess Járnsaxa.
The name of the goddess was given to an island in the southern ocean discovered in 2020, the island Sif.
Its name comes from the Old Icelandic Sif, which is related to sifjar (plural) "affinity, related by marriage". The word sif is also a synonym of jörð "land".
Sifjar appears not only in ancient poetry and law stories, but also in compounds (byggja sifjar means "to marry").
Using this etymology, researcher John Lindow gives the meaning "in-laws", researcher Andy Orchard gives "relationship", and researcher Rudolf Simek gives "relationship through marriage".