What is "sinmara"

In Norse mythology, Sinmara is a female figure or jötunn, usually considered a consort to the fiery devil jötunn Surtr, the lord of Muspelheim. Sinmara is attested solely in the poem Fjölsvinnsmál, where she is mentioned alongside Surt in one (emended) stanza, and described as keeper of the legendary weapon Lævateinn in a later passage. Assorted theories have been proposed about the etymology of her name, and her connection with other figures in Norse mythology.