In Norse mythology, Sinmara is a female figure or jötunn, usually considered a consort to the fiery 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.
The etymology of the name Sinmara is obscure. The latter element of the name, mara, may be a cognate to "(night-)mare", as suggested in the Copenhagen edition of the Poetic Edda (1787-1828) annotated in Latin. Here the sin- element is identified as meaning "sinew" or rather "nerves", so that the total phrase comes out as "nervous (or nerve-afflicting) nightmare".
It has also been proposed that the sin- element may refer to sindr (Old Norse "cinders").Rudolf Simek opines that sin cannot be related to the term sindr, while this would equal a "meaningful interpretation in regard to the colour", he theorizes that a more likely interpretation is "the pale (night-)mare", noting that this would fit the wife of a fire jötunn.
Adolfo Zavaroni and Emilia Reggio suggest the interpretation "Perpetual-incubus." The sin- element is here theorized as being the same as in the male name Sinwara, found in a runic inscription on the "Næsbjerg brooch" from Denmark, Old High German sin-vlout "great flood", Old English sin-niht(e) and Old Saxon sin-nahti "eternal night", and Gothic sin-teins "daily". J. Fibiger assumed the meaning "the great mare" based on the Sin- element in the Old High German word Sinfluth "great flood" (a variant of previously mentioned sinvlout).