In Norse Mythology, Sigyn is a goddess from Aesir lineage. She is the wife of Loki and the mother of Nari and Narfi
She is mentioned briefly in Icelandic sources: the Poetic Edda, compiled in the thirteenth century from older sources, and the Edda of Snorri, written in the thirteenth century.
Sigyn is only associated with the myth of Loki's punishment for the murder of Baldr, where, as a faithful wife, she collects the snake venom dripping on the face of her chained husband in a bowl, in order to alleviate his suffering. However, she must regularly empty the bowl when it is full, letting the venom flow for a few moments on Loki who is writhing in pain and then causes earthquakes.
Sigyn is depicted on the tenth-century Gosforth cross, and her earliest mention comes from the ninth-century scaldic poem Haustlǫng, preserved in Snorri's Edda, suggesting that she is an ancient Germanic goddess and not a recent creation.
Sigyn is the wife of Loki according to the epilogue of the Eddic poem Lokasenna, and the Völuspá 35. In Snorri Sturluson's Prose Edda, Sigyn is introduced in chapter 33 of the Gylfaginning part as Loki's wife and mother of Nari and Narfi. In chapter 16 of the Skáldskaparmál part, a kenning (a kind of periphrasis specific to Norse poetry) given to designate Loki is "Sigyn's husband".
Sigyn is presented as an Aesir in Snorri Sturluson's Edda. In the Skáldskaparmál part she is mentioned among the Aesir who sit at the banquet for the visit of the giant Aegir. She is also listed as an Aesir in the Nafnaþulur preserved in the Edda of Snorri.
The scaldic poem Haustlǫng, attributed to Þjóðólfr ór Hvíni and dated to the ninth century, is preserved only in Snorri's Edda, and the author employs in stanza 7 a kenning referring to Sigyn for Loki and his torment: farmr Sigvinjar arma ("load of Sigyn's arms"), attesting then to the ancient nature of the goddess and the associated myth.
Indeed, the only myth associated with Sigyn is that of Loki's punishment, where as a faithful wife she stays by his side to collect in a bowl the snake venom that should drip on the face of her chained husband.
Sigyn is mentioned in the prose epilogue of the Eddic poem Lokasenna. In the poem, the trickster god Loki insults the Aesir gods at a banquet. The epilogue tells that following this behavior, he hides in a waterfall having changed himself into a salmon.
The Aesir seize him and chain him with the intestines of his son Nari by transforming his other son, Narfi, into a wolf who tears him off. The goddess Skadi ties a snake above Loki so that its venom drips on his face.
His wife Sigyn, sitting next to him, holds a bowl to collect the venom, but she has to empty it every time it fills up, letting some of it drip onto Loki.
Loki's torment is described in chapter 50 of the Gylfaginning part of Snorri's Edda. However, the reasons for Loki's punishment are different from the Lokasenna; in Snorri Sturluson's Edda, it is for having coordinated the murder of the god Baldr and having prevented him from returning from the realm of the dead, Hel.
In this chapter, the author describes in more detail the capture of Loki, transformed into a salmon and hiding in a waterfall. The Aesir also capture his sons Nari and Narfi, and transform Nari into a wolf that tears his brother Narfi.
With Narfi's entrails they tie up Loki, and Skadi hangs a snake over the god so that the venom drips on his face. Sigyn collects the venom standing with a bowl that she has to empty regularly, letting venom flow over Loki, causing him to immeasurable pain. Loki remains chained like this until the prophetic battle of Ragnarök.