From Íslenskar Þjóðsögur og Sagnir, vol. 3. collected by Sigfús Sigfússon, p. 269.
Flagðaspá (‘The Prophecy of the Ogress’)
In previous ages there was a man from Svarfaðardalur looking for sheep late at evening in the fall in a distant valley which runs from settlement. There were two troll-women who lived in the hillside on each side of the valley. He hears when one of them says “How is the winter biting you, sister?”
“Both ways, sister,” the other declared. “Or will the bug hear our speech which flutters below in the valley?”
“Yes, yes, that doesn’t matter, sister. And let me hear about the first month.”
“Then you will tell your plans, sister.”
“So shall it be.”
Then the one who spoke later started to speak:
“Tight grinds Frosti (‘Frosty’), the mountains are covered in snow.”
Then the other one says:
“I suspect that Skuggi (‘Shadow’) will battle him and wet the snow.”
“Ljósberi (‘Lightbearer’) will release the liquid of the snow from the fields.”
The other answers:
“Blóti is though better, the veins of the mountain will bleed.”
“Snow-white will be Svanni¹, sea-ice and roofs of snow.”
But the least of them is Einberi (‘Single-Carrier’), he is not nice to widows, sister.”
The man remembered what they said in his memory and used it and it is said that everything came true. The first month they called frosty (Frosti), because then it freezes first. The second the shadow (Skuggi) of the shortening days. The third light-bearer (Ljósberi) because the sun got higher. The fourth “blóti” because of the ancient Þorrablóts. The fifth “swan” because of Góa² and the sixth single-carrier (Einberi) because he was the only one left after the winter, but in it there were many boat- shipwrecks at sea.
¹ Usually a poetic term for a woman, but here appears to be a personal name of a being named “Svanni,” which seems to be a diminutive from “svanur” (‘swan’).
² A month in the old Icelandic (Góa) and Norwegian (Gøj) calendars corresponding to late February to late March.
The Old Icelandic calendar had six months of winter, here described as jötnar or some other troll-like being except, curiously, the two which are usually named for jötnar (Þorri and Góa). The names correspond as follows:
Frosti is named as a jötunn in a number of sources, and is related to Þorri and Góa in Ornkeyinga saga (Hversu Noregr Byggðist places Jökull ‘glacier’ in that position). I do not believe any of the others are attested as jötunn names.